Apple's got a new price on a refurbished iPad (that's an iPad 1, not the latest 2), and it's likely the lowest official price you'll ever pay for the tablet. $299 is the new magic number, for a 16 GB iPad Wi-Fi. Of course, that presumes that the unit will come back into stock, but it likely will before long. That price is the lowest available from Apple, so if you want to get an old iPad for cheap without going the used route, that's the best way to do it.
The 32 GB Wi-Fi version is available for $399 refurbed, which is cheaper than new, but I'd say unless you really need the extra memory to the detriment of everything else, a brand new iPad 2 16 GB is only a hundred smackers more than that. Probably worth the extra cash in that case.
Other sites will occasionally have the iPad for even cheaper than these prices, and of course there's always eBay or Craigslist if you want to pick up a used unit. If you're looking to buy and price shopping around, good luck!