Don't cheap out. The PCP world is def a buy once cry once then get the bug and buy and cry some more thing. Budget a good air compressor and tank with a drier if the compressor doesn't have one built in. The recommendations for a .30 or .35 for Yotes are good ones. The .30's can be quieted down with a moderator pretty well, don't know about the .35s. You will def want a moderator to stay discreet. These are loud enough to draw attention without.
I just picked up a new RTI P-3 in .25 cal but winter and all I won't be able to mess with it for a while yet, they offer it in .30 but they are not semi auto. There are a bunch of good ones but semi auto limits choices. Personally I'd avoid the AEA and Hatsan stuff. Evanix maybe? See folks asking questions about them but not too many complaint threads unlike the other two. Never owned a SA one so I'm not much help.