I went through a phase of snapping new unused chainrings up whenever I saw them. IIRC I bought 2-3 full sets of MTB rings and 1 pair of road rings, all for no more than £25 a set, all Shimano. With the current price rises this has paid off well. I have a draw full of rings to use… 🙂
I bought 2 36t middles just before the prices went up too, fitted one to the Pitch with a bashring which liberated the 32 & 44t it came with. I've just fitted them on my Inbred.
I've done a lot of this stuff for the last few years and I can't remember the last time I paid good money for a cassette or chainring, just the odd chain.
Best bargain was a £5 wheel I picked up. It had a bent rim, but a Deore hub, cassette and disc fitted. The hub I built into a decent wheel with the spokes and rim I already had, the cassette took a new chain (it looked nearly unused) and at the same time I fitted the 2 Pitch chainrings and a nearly new X7 mech (Classifides)
Working it out, I got a good, well rebuilt, back wheel, a brand new chain, 'new' middle and big rings, 'new' cassette, and 'new' rear mech for a total layout of just under £45. 🙂
You just gotta keep your eyes peeled….. And be a bit lucky. 😉
It does look like the prices are rising, but there's the odd cheap one about still
http://cgi.ebay.co.uk/Shimoan-Deore-SG-X-M9-S-22-22-tooth-chain-ring_W0QQitemZ280417961955QQcmdZViewItemQQptZUK_sportsleisure_cycling_bikeparts_SR?hash=item414a3687e3
EDIT
I'm running out of chainrings now though. I think I have one more well used middle and outer that might do a few miles, and that's it… 🙁