I see you guys are talking about pumps ... and since Tyger hasn't gotten in on this yet, I will.
Get a Blow-back Spyder clone (or spyder, or similar) play with it for a year (no need for nitro or anything, but I'd get a reg. Not to be confused with an expansion chamber. This will give you consistency and keep you from shooting hot, even with co2). After a year or so of playing with that setup, then get a pump. That will help your aim and your budget. Then, after a year of playing mostly pump, and a bit with the semi, you could upgrade to a super high end tourney marker that shoots 8million bps and will tell you the temperature, or something like that ...
Manning, was my grammar and spelling up to your high standards?
-Micah