If you're really, really, really tight on money, then I would recommend a Lancer Tactical ($120).
I've had a Lancer Tactical CQBR Mk18 for more than a year now, and it hasn't failed me yet (4000+ rounds). It comes with a 300rd hicap mag, and a 8.4v 1200mah nunchuck battery. This allowed me to get all the gear I needed to play for under $200. It's a good way for you to test the waters for airsoft. I would not recommend upgrading the LT guns at all, since it's more of a use-it-until-you-break-it gun.
However, I still agree with the above comments. If you're buying cheap, expect it to poop out on you in under a year (I've heard some stories of cheap guns breaking in under 1000 rounds). If it breaks, don't bother saving the thing. Strip it for parts to subsidize your next purchase.