I use Sorenson 3 encoded Quicktime movies for my website. I set the quality to anywhere between 65-70%, depending on what is in the footage. Then I limit the data rate to around 90-150 K/sec. This part does sacrifice some quality, but it is adjustable so you can tweak it to your liking.
For something that is 2500 frames long, you're still going to get a pretty hefty file. You're just going to have to bite the bullet and make it large download. One way to cut it down is to reduce the frame rate (i.e. use 15 fps instead of 30 fps). Yes, you'll lose some smoothness to the motion, but if you want a small file, you'll have to make some sacrifices.
Realistically, as long as you warn the user that the download is large, they'll be fine with it. Just make sure the animation is worth waiting for.