We parked right at the airport. Secure lot, well lit. The parking lot shuttle will follow you to your parking spot and will drop you off at whatever airline you're taking. Cost was something like $30-mumble-mumbleUSD for a week (I think it was something like $37/$38USD, but we had a coupon and we were gone six days), plus a couple of bucks for the shuttle driver for loading the bags.
Were using the parking at the airport. You can get a coupon off thier web site for the Buffalo Niagara airport it saves you a bit of $$. We are in the same boat as the OP we dont want to get a hotel we just want to go
Do you need to make reservations for Sunpark? I saw you can for an extra $3, not a big deal, just didn't want to give my credit card on the net unless I have to.