there's good guns available from vendors who are searchable on google, they will probably also do an age check when you purchase the guns, but can't verify you for the forums.
600 is a reasonable budget... set aside at least 350 for gun, battery and charger at the minimum. budget up to 100 for eye protection, though I recommend the fan goggles at 160-200 range, much better for fog resistance. Some extra mags if you're going with an m4/m16 style gun mags are cheap... 50-60 can get you 5 more midcap mags.
That covers the basic stuff you need... beyond that... you should consider if you don't already have:
good boots with good ankle support
some way to carry water onto the field
some way to carry ammo/mags onto the field.
what you decide to use or get to fill those purposes and what it costs is up to you.
Forget the pistol for now. You can do without it if you are budget limited. Don't buy shit guns and waste your money. You have a good starting budget, but be smart with it. Good pistols start in the 200$ range for just pistol and 1 mag.