My experience is that a 10/22 sporter is normally a very good shooter, but with a trigger job, and a new barrel (
http://www.gmriflebarrel.com/20-stai...porter-barrel/). It takes about $200 and a few minutes to make one into a fine squirrel rifle.
For a bolt action it is hard to beat a CZ 452 for the price ($400 or so), or a Remington 541 T (a bit more). A friend of mine shoots a 452, I shoot a 541 T, and they both shoot great.
When I take a walk in the squirrel woods it is a toss-up on whether it will be a modified 10/22 or the 541 T that goes with me.