For air stick to about £30-£40 for a new aluminium 3000psi cylinder
(Fibre 4500psi will set you back about £80 second hand or £150 new)
Hopper around £30 to £80 second hand for a force feed one such as the halo to rotor
Remember a pod belt and some pots
After those you should have an easy £200+ spare for a gun, do see what packages are about but don't stick to a basic package when buying new, ask what prices you can get for buying a few items
Every shop will come up with some form of deal, but keep an eye out on new vs second hand