To be practical, you really don't need 1000fps to shoot in the garage. For what you are wanting to do, you need the variable power from a pumper.
The Airmaster 77 would be the best choice for what you are wanting to do. 10 or 12 pumps and a good head shot would be needed for squirrels, but for plinking and indoor target shooting you shouldn't need more than 3 to 5 pumps.
It's tempting to get one of the more expensive guns for FREE, but the Airmaster 77 will probably be your best bet for all-around versatility.
But that's just my opinion.