Asked a similar question a few days ago myself on the wanted section. Bought some Nutrak tubes on Ebay, quality is good for the price, weigh around 180g. Paid about £2.30 ea inc postage. You can buy cheaper tubes but these have had good reviews.
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Get yourself along to one of those sports centre sales. They are advertised in Cycling Weekly, (or my own publication Cycling Weakly). Stuff like GT85 (still the best smelling bike lube you can buy), tyres and tubes are CHEAP.
You can also pick up the occasional retro bargain. I once picked up a pair of XC Pro hubs for £5!