SusanFromVermont Loc: Southwest corner of Vermont

Welcome to UHH! Your bird photos are great, keep up the good work.

Not familiar with Canon cameras, so cannot make any lens recommendations. But I do concur with the suggestion that you look for a pre-owned lens. Places like Adorama, B&H, Cameta, and KEH have excellent reputations for quality, prices, service, and returns policies. Plus they have clear standards for how they grade the pre-owned gear. eBay lets its vendors choose whether or not they take returns, but if an item is not as represented, eBay has a return policy that vendors need to follow. [I'm not familiar with how it works, but it ought to be explained on the site.] There are plenty of great items on the site at excellent prices.

As others have pointed out, you do not need a 500mm lens to get the appearance of having used a 500mm lens. That is because of the "crop factor". This means that a full frame 300mm lens on a full frame camera will show the same magnification of the subject, but more of the background, than a crop sensor camera. This may mean that for a close-up shot taken on a full frame camera, more cropping may be necessary. On a crop sensor camera, you get the same magnification, but the sensor only captures the middle part of the full frame lens, essentially cropping it in camera, therefore less need for cropping in post processing. So you could purchase a full frame lens, either zoom or prime, that takes images at 300mm and they will be cropped in camera to appear as though they have the reach of a ~450mm lens.

If you want a true 500mm magnification, then you are talking about much more money. But it is worth looking online for a pre-owned lens. The 150-500mm lens from Sigma comes in 2 versions. The Contemporary is less expensive, supposed to be a decent lens, but the more expensive Sport is much better. I do not know anything about the other companies' versions, but you could use the UHH search function to find this type of discussion of choosing a lens. And keep in mind that these big lenses tend to weigh in at around 5 pounds.