for a cheap first, id go with a crossman pump and shoot lead pellets, not BB's from it...
if you want to get a nice one you can get one of the more expensive pellet rifles aka "adult air rifles" that are 100-300+..
reason i recommend shooting pellets is accuracy...yes they cost a little bit more...but pellets are pretty dang accurate even from the cheap crossman pump guns...that way, you can teach the fundamentals of shooting and know that the gun actually shoots pretty well opposed to BBs which have a terrible flight path and can be erratic...