well, last I checked none were really cheap :tonka: , and they are all booked anyway. unless you can get in due to some cancellations. there is claybanks on the other side of stony lake, they might have room but that is about 20 minutes away. do you know anyone up here with a cabin or cottage? anyone already camping up here? this late in the game, that might be your best chance.
as far as getting into the dunes, all you can do is try to get a voucher. they might have some and might not, but if they are all gone, you should still be able to get someone to tow you in.