I'm a big fan of Qwikpark. They send out 1 day and 2 day free coupons, with the rest of your time at $7.50/day. Sorry this doesn't help you with a long stay. Plus, their coupons are always available for printing at qwikpark.com. Just used a 2 day coupon for a 3 day stay and paid $7.50. Have used 2 day coupons before and owed nothing.
I always use friends or family for long trips, because I don't want to pay to park my car. And I tell them I'll repay the favor.