Always true Paul, and surely a good question to ask. Expectations need to be set up front. There's always that fine line between what you, the photographer thinks it's worth, and that of what the customer/buyer of the product thinks. Sometimes when a fair price can't be agreed upon it's just as well to walk from the job. Especially if you sense that the customer doesn't see the value of the service or product you are providing, and a customer like that can make your life miserable should you decide to take the job.

There's some good comments so far. Reading your responses, here are some issues to consider / address in a quick written agreement:

Total price
Expected hours to be shooting, in hour ranges, such as 2-4 hours - cost $x; 4-6 hours, cost $y, so forth
Delivery timeline - initial drafts, final edits / finished images, specified by estimated dates, or days following shoot
Delivery format - JPEG, upload website, physical media, email transfer, etc
Image ownership - are you hired to shot images for them for images they own? Or, are you licensing images you own for their uses?
Payment schedule - all up front? Half now, half on delivery? Other? Specify how payment will be made too.

Personally, it sounds like they're hiring you to shoot for them, as in they own the results. If this is the situation, you should state this expectation as well as specifying how you can use the resulting images too, such as social media, personal website / portfolio, etc. As a hired photography, just cover the technical logistics, deadlines from the list above and set a total price, paid 50/50 to start and upon delivery, or a lumpsum at the end. Also, put-in other comments covering the scope of your work being the photography, not the dress selection and such, maybe covering where the shoot occurs, as in, at one place of their choosing / date with a specific start time.

Think about 70 dresses, if you waited for the preparations and shot maybe 5 / 10 versions of each for 15-minutes waiting and then shooting, that's 17-hours, likely a multiday event if done sequentially. If all the dresses were ready, it still might be a 5-minute average that would be 6 hours if working that slow and deliberate. Take your total shooting time and allow the same duration to process and prepare the images in determining a turnaround deadline.

Outside the technical logistics, seek to confirm what shots they want. I'd think a full-body frontal, maybe a side / three-quarter full length view, as well as one or more detailed / close-up shots, especially the shoulders and neck-line. Do they want all in a portrait aspect? Mixed landscape, portrait and square? What ratio? 1x1, 3x2, 5x4, 19:6, other?

CHG_CANON,
Hello Paul, Thank you for the valuable information, a lot of information to cover. I am meeting with the customer Monday for further discussion to confirm exactly what they expect and what I have to offer.
I have had a previous conversation with the customer and I really don’t think they know what they want except pictures to upload to Esty so they can sell these dresses. I’m thinking initial set up, time to shoot, hopefully limited editing, full length view, digital copy, and now that you mentioned it:
“specifying how you can use the resulting images too, such as social media, personal website / portfolio, etc.” This is a great suggestion for a future. Thank you and enjoy a great day and wonderful day!

It really is a lot to unpack - but critical to your success. Everyone thinks that commercial photography just requires shooting skills. Taking pictures is about 20% of it. The other 80% is client management, unimpeachable customer service, how to anticipate disasters and plan for them (equipment and staff redundancy, contingency plans etc), and how to say no to a job you are not qualified for. Sorry for my ominous tone, but I would have given anything to have heard this when I got started back in the late 60s. Good luck with this. Something worth considering is handing this off to a pro, and ask to be an assistant in return for the referral. You will learn an amazing bunch of stuff about the profession, and you will likely have a very happy customer that understands that you were looking out for their best interest.

Truthfully, NOBODY can tell you what to charge! Your charge must be based on your overhead, costs of sales, your level of competence in photography, and the profit margin you must establish whereby you can be reimbursed for yoor costs and materials and earn a profit for your business or yourself. Another factor usage is the number of catalogues that are going to be distributed and where yo image will show up.

Concerns about copyright and usage get are valid but many "bridal fashion" shoots are not for long-term usage. Style and modes change from season to season in man cases.

If are actually considering going into business, a solid business plan shod be a prerequisite to establishing prices. It is generally NOT a good business practice to ask inquire about the cleit's budget is and try to squeeze into it.

Just out of curiosity- Why mannequins- what not live models. Effenceicy wise, it takes less time for the couturiers to dress models as you shoot rather than pin-fitting dresses, and dressing and undressing mannequins. If I know how to pose models to emphasize the lines of a dress, drape gowns and trains, and arrange veils and flowers you are ahead of things. Also, do you know how to light and bring out fine detail in weddings gowns?- they can present many issues- white on white, embroidery, lace, thin tulle veil material etc.

I know little, or next to nothing has been said about exposure and lighting, but you did say you will use some light(s) Obviously, I assume most or all the dresses will be white, and whites can be very tricky, not enough and the whites look gray, too much and you'll blow out the details. And surely, the details in the wedding dresses are critical, and must be perfectly lit, and perfectly clear. I don't know what kind of lights you'll be using, but you'd want a large light source, even bouncing off a white wall or reflector behind you can work nicely. This will help distribute the light evenly without hot spots, or blown out areas. I shoot with speedlights a lot on jobs, and almost always I'm bouncing into white reflective umbrellas. And sometimes all you need is half power, or even less...just a pop of light is often enough. I would not recommend using a hard, unmodified light source, such as direct flash. If I were shooting this job I'd be going in with a mental starting point as far as my exposures, maybe the following: f/6-3 or f/7.1 to maximize DOF on the details, ~ 125 second, and one or two speedlights bouncing into the umbrellas, set at the starting point of half power each. Grab your one or two test shots, check the histogram, and just adjust your light(s) up or down on power as needed. (or move them in or out slightly until you're happy with what you see) Once you dial that in, and as long as you maintain the same distance of the light source to the subjects all the rest should be easy.