Are you asking if you can find one "really cheap" as in "below retail"? I'd love to tell you what you want to hear, but c'mon, let's be realistic here. Wii's are still extremely high in demand and difficult to come by - period. Going to an auction site like eBay will likely get you one for sure, but you'll pay a premium for it. Any store that happens to still have some in stock are probably bundling it with hundreds of dollars worth of extra games and warranty so you end up paying $500-$600.
You can try to win one in a contest as one person suggested, but at the moment, finding one at retail ($249) is considered almost as fortuitous. One method I would recommend to locate a Wii (sans bundle) should you choose to accept this mission is to get yourself a Saturday Preview of the Sunday paper which contains all the ads. Flip through the ads for stores which carry the Wii (like BestBuy, Circuit City, Tartget, WalMart, K Mart, GameStop, Toys R Us, etc). At least one of those stores will usually have stock on any given Sunday. And be prepared to go early and wait in line before the store opens.
Fortunately, Nintendo just recently announced that they will be ramping up production on the Wii (why haven't they already?!), so it should become easier to find one. But even then, it'll be months before you'll start seeing any "used" ones at GameStop. Good luck.