AFAIK the reason why old Tamron and Sigma lenses are so cheap is that they often dont work on newer cameras. So I wouldnt exactly jump in excitement about such offers.
The situation has a bit improved since both Tamron and Sigma have introduced ways to upgrade their lens firmware, allowing them to be more compatible. However there is of course no guarantee they will actually still actually make new firmware upgrades for their old lenses in say 10 years from now.
I personally used the 55-200mm on my APS-C entry level DSLR, back in the day. But I wouldnt recomment it for wildlife. Because at least mine was soft at 200mm, even if stopped down. It was very sharp at 55mm up to about 135mm though.
Personally I would pick up a camera with a good autofocus system, and a lens with good reach for wildlife. Like Nikon D7100 and AF-S 200-500mm f5.6 VR.