Wow, that is dodgey. They could at least go to a cheaper place so they could afford it. I have got 2 engagement invitations in the last few weeks and I find it very suprising that they are both BYO and the invitations were nothing to brag about either.
We put alot of thought into our invites and into our wedding and engagement. We saved up every last cent for it too. I think if your invited as a guest at a wedding, you should be treated like a guest, not a customer!
Also, I think all these people asking for money as gifts is a real joke. (IMO!) I prefer to buy a gift, to give money is just like asking to pay for part of the wedding. But thats just my opinion.