ON or near campus:
The Courtyards
These are a little further away from UK, but on or near a busline
Tarleton Crossings - I hear these are nice, in your price range and accept pets.
Breckingridge Court Apartments ($560 a month, and accepts pets)
(Use to be pretty nice, but haven't been inside of one for a long time)
Brandywine (Under 600 a month and accepts pets)
Harrods Point Apts A little more out of the way, not for sure if they are on busline.
Raintree
Fairington (I think you would qualify for this - it's a HUD apartment ran by Gene Glick, and they really take well care of their apartment communities. Rent based on Income)
Good Luck in your apartment search and Welcome to Lexington!