Ive got 2 plants on the go and the total cost for me was less than £40.

Tubs cost me £2.49 each
Air tubing cost me £2 for 4m
Air stones 99P
Nute's £4.98
Flo's £7.99 each got 2 so far 40w each
Seeds got for free out some good weed
Aluminum foil £2.10 that was for 20m(the maylar cheap option)

In total that is = £30.04

Im adding a couple of CFL's to the closet soon.

So as you can see it doesnt cost that much for a basic setup really.

Heres a couple of piccys of my hydro's