It wasn't cheap, but have you looked at the Cabo Surf Hotel? in 2006 we found their prices to be low compared to other hotels (don't know their 2008 prices, sorry).
Another option is to rent out a house that is on the beach at Costa Azul and just have a wedding right there on the beach! This place comes to mind: Casa Sueno - San Jose Del Cabo, Cabo San Lucas Luxury Villa Rental
We actually saw someone get married there. You can rent out the whole villa for the week. The owner is the guy who married us, actually, but you can do the booking through the company I think. It's not a fancy resort but it is beachside and the pool is very cute too.