Why not tell him? If he's that close of a buddy, he'll understand that it's a financial hardship for you and others, and maybe he'll offer to help out.
Personally, I think the whole wedding thing is ridiculous, at least with regards to the wedding party. There are so many expectations placed on these people at the whim of the bride and groom it's ridiculous, particularly when you consider how much money most of those expectations cost.
Your friend has decided to have one of the most expensive wedding options for those in the wedding party, which to me is asking more than a person should.
If it's that important to them, they should offer to help out with the costs. If not, tell him you're sorry but it's just too expensive.