80% sounds like a lot! The most I've seen with any of my vendors so far is 50%. See if you can negotiate with them to give 50% instead of 80%?
On another note, do you happen to have the 2009 price list for Del Cabo Event Design? I can only find the 2008 price list and I want to make sure prices haven't jumped a lot before I contact them. If you have it, can you email it to me?