Being a noob myself here is what I bought at first.
Gun $410 -you can get away with the Hi-cap for your first year
Paintball mask (already owned) $40
Boots (already owned) $80
This is the bare essentials. Make sure you do not cheap out on eye protection or boots. They will keep you safe and injury free.
Now sinse then I have bought two other aegs, a gbb pistol, a box of 8 mags, a grenade, and a whole bunch of accessories and upgrades for the aegs.