you should be able to pick up a stock LED for £350 used
But you won't find one that hasn't got upgrades,
Basically the Aardvark bolt kit (red or blue) adds £75, the front reg (trinity) adds £50, and any other bits are basically a bonus.
Personally i think the LED is the way to go, because if you want the Mayhem Tigers to put an eye in, (and you will) then that makes the gun LED again anyhow.
If you bought a used LED, for say £500 and paid £180 for the eye, you've got one of the fastest and most accurate markers out there. Basically a paintball machinegun, that shoots strait!