Think long and hard before you buy your first marker. If you get bitten by the bug, it's the quickest descent into bankruptcy I've known
. Whilst, starting cheap may seem like a good idea, there's a good paintballing adage out there "buy on price, buy twice!". If your sure Paintball is for you, even just playing rec and walk-on, I'd recommend going for the best spec or upgradeable marker possible. Sniper speaks wisely when he recommends an Impulse, because they are cheap to buy and have a huge range of performance and aesthetic upgrades. They're also dead simple, and shouldn't require any tom foolery to adjust velocity etc (I'm technophic so a cocker was beyond me until now).
An Impulse is likely to last you a lot longer before you want to upgrade to another marker (unless your a vain tart like moi), and you can pick up nearly new ones very reasonably at the moment. Also a lot of upgrades can be bought for good prices (although I-frames still command good money cos they rarer than rocking horse poo). With a few upgrades these markers can fire as fast as you could pull the trigger (up to 25 bps me thinks in Vision form), and importantly consistent, which means you haven't got to be a great shot to bring the pain.
I can only speak as I find, and don't want to put you off other markers, but I would also recommend the Impy as a starting marker. I'm sure people can give you plus's for the Bonedaddy and others, but for the flexibility of upgrades that can take you all the way up to Pro killing machine. My first marker was an Impy, and despite catching the Angel Bug and owning various other must have markers, I still went back to shooting a fully tricked out Impy. I think you can get good and bad in any marker (I had an Ir3, which was very unreliable, perhaps just a "bad one"), but with my Impy, I don't touch it in between practice days short of airing it up, (and others here can vouch) that it always chronos with +/- 3 fps. Last training day without showing it an Allen key it was chrono'd every shot between 294 and 296. With that level of consistency your shot grouping should always be good over distance.