yeah, I had a hard time negotiating with them too. I was able to get them to lower their deposit, so you might want to consider trying that.
I did have them do our wedding cake..it cost me $100 it was a little crappy cake and didn't taste very good. We just wanted something to cut, not necessarily for our guests to eat. We chose a buffet though and there were tons of yummy desserts in the buffet, and the food was very good.
Also, we did open bar on a consumption basis and I think that saved us a ton of $$... a lot of our guests had been partying the 3 nights leading up to our wedding, so they didn't drink much at the actually wedding, so you might want to compare per drink prices to the per hour open bar prices.
Let me know if I can help at all...you can always pm me...good luck! The Sheraton is beautiful!!!