If you want "real" reflectors - and JTSmith's advice is on the money as far as improvising - the best thing to do is watch places for sales. eBay is so filled with people with more money than sense that it's hard to get a deal even on *used* stuff anymore, but for some reason reflectors occasionally go on mondo clearances.
I have a 22" collapsible ZipDisc that has *four* reflectors (silver, gold, white, black) and can also be a translucent light screen. I paid $20 for it at Calumet Photo during a big old sale on lighting accessories. I also have an *enormous* collapsible reflector (It's more than four feet across) which has gold, silver or white interior (velcro swaps) that I got for $39 marked down from nearly $200. (I couldn't pass it up: I thought I'd sell it if I decided I didn't need it. It would also make a decent emergency shelter.) And at the same sale I got two 36" umbrellas with removeable black/silver reflector material for $15 ea. And, in one of the few pluses of living in Chicago, I got all this at their retail store, so didn't even have to pay shipping.
I'm not trying to make anybody jealous (it's not like I actually use all this very often) or make suggestions on a lighting kit, just to illustrate, if you'll pardon the pun, that when photo stuff goes on sale, it can really go on sale. I've gotten some fabulous deals from Background Outlet in Chicago, as well - yards and yards of firecloth for $20. (My wife, who's a dancer, tells me that she can't buy raw fabric in a fabric store for what I've paid for some of those backdrops.) Their website usually has a clearance and an auction section. (Calumet's always has a sale spot and often has clearance buys as well.) Just keep checking around. You'll find stuff.