VFC, and G&P would be good bets. CA can also be found under 600 infact almost all good rifles can be found under 600 or less in the classifieds. Get "Age Verified for her pleasure". Seriously the deals amazing. CA m15A4 (M4) UNDER 500 fully upgraded used or around 450-550 brand new!
Crane stock isn't what you want those magpul buts stocks don't house batteries. Try out a madbull buffer tube w/ battery space can be found on airsoftparts
Good luck and welcome to airsoft.
EDIT: G&G aren't bad but for your budget you can do much better and KWA are good and I've heard little bad about them
But really want to save money? Check out King Arms M4A1 great rifle at a great price.
Originally Posted by FirestormX
I know that isn't really what you asked, but it's the internet, and I like to type things that don't matter.