I photograph a lot of dogs, and there are a lot of lenses that will do a nice job for you indoors. I used to own a Tamron 28-75 f2.8, which I really liked. It's a perfect range for indoor pet photography and falls well within your budget. The only reason I sold mine was that I also used it outdoors, and the slower focusing had become a problem. Indoors, though, it's terrific.
Probably my favourite indoor lens for my dogs is my Canon 60 mm macro lens (f2.8). Its close-focusing capability opens up some interesting creative possibilities. I also have a friend who produces great images with his 40 mm pancake lens. Both are well within your budget as well.
Good luck with your choice!