The best solution would be ScanCafe, provided they are 35mm slides. Large slides cost a lot more to convert. I had over 1,000 slides converted by ScanCafe, and they did an excellent job.

As soon as they scan the slides, you can view them online and eliminate the ones you don't want (up to a certain limit). Eventually, they will send you a CD or a DVD with all your pictures, but first, they will let you download all of them.

Of course, you can do the work yourself, but it is "work," and it can be overly tedious. I doubt you would be able to duplicate the quality of ScanCafe.

Twice I’ve been in your shoes. The first time was when my ex-husband passed away, I inherited all his pictures. Since he had pictures of our kids, I knew they would be as important to them as they were to me. I’m a scrapbooker, so I combined his pictures with mine and those my mom had, scanned the best ones, and made scrapbooks out of the original pictures. It took me a year to finish this project. These are the most treasured items in my home.

In addition, I got all the old pictures of his family and slides from Europe when he was stationed in Germany and I was with him. For the slides, I took the best ones to Walgreens and they made some beautiful pictures for me.

I scanned the old pictures and put them on discs for his brother and sister and returned the photos to them. Now his sister is moving from Michigan to California and she has asked me if I can “do something” with her pictures.

I have no idea what a project this will be because I don’t know the size of her collection. I had planned to create a digital scrapbook of the old pictures I previously scanned and I may do that with her pictures as well if a traditional scrapbook is too daunting.

For me and my family, we LIKE the physical display of our pictures. It’s a lot of work; but so rewarding. It’s not for everyone, but that’s what I would do.

I’ve read all the responses and you got some good answers. Good luck in this quest!!

EDIT: I just reread your question and this doesn’t really answer you.

Shop the internet to compare prices, then go to a local processor, if there is one in your city, and ask if they can match, or come close to the prices you find.
The local processor I've been using for a while, does make it worthwhile to use their services. There is also a bank of 4 computers, with high quality monitors and image editing software, available to use, free of charge, which I think is fairly common these days.
I believe most internet services, these days are about equal in quality, so the attention, and services, I get locally helped me decide, when I ran across my grandmothers, and her sisters photo negatives from 40+ years ago.

Be sure to safely store the original slides and reels (in a cool, dry, safe place).
Digital copies are likely to get lost or become unreadable within 5-10 years.

As yourself: how old is the oldest still-readable computer file now in your possession?
And how old is the oldest photograph in your family album?

I've been using computers since the 1970s, and my oldest file is probalby from the
1990s. Most of media I used to store files (1/2 inch tape, 5.25" floppies, VHS tapes,
QIC tapes, Zip drives, Syquest removable hard drives, 3.5" floppies, diigtal linear
cartridge tape, etc) are now unreadable or you can't buy a drive for them.

Magnetic regions on spooled tape bleed through layers (if the tape isn't rewound
regularly), and somtimes the rubber rollers in cartridge tapes turn to goo.

One shouldn't expect that TIFF, GIF, JPEG, PNG etc. image file formats will always be
readable. New vesions may introduce incompatability.

I have data stored inside of tar and cpio and tar archives, and compressed with compress,
zip, pkzip, gzip, etc.

Trying to read old media is real Tower of Babel -- even if the media is still readable and you
can obtain a drive that will read it.

I assume you want these photos to stay in your family for future generations. Digital = disposable.

I would agree with your advice to preserve the originals, but I would also suggest that the archival quality (or lack thereof) has more to do with the media it's stored on than with the integrity of the files. I have stored digital images and other important files that have progressed from 5 1/4 floppies to 3.5 inch floppies, to CDs, and memory sticks, as well as having kept virtually all of my images the past few years in original form on the SD cards. Once a year, I transfer my oldest files to newer media - for example, I have no floppy disks at all any more, and have both CD and SSD versions of an entire generation. I also have backup hard drives, both SS and spinning.

It's not perfect, but it's better than relying on only one form of backup.

Andy