That's a tough one. Under $1000 thermal that will detect an animal at 500 yds, probably not. But for less than $2000.00 you can get a new FLIR Scout ll 320 that should give you an honest 3-400 yd. detection in ideal conditions. Not the best image, and not the latest technology, but they work.
I have tried a few different scanners and I still use a Scout 640 because of the reliability.