The scary thing about this is.... it is early in the planning stages and the future bride & groom may have already brought about some dissension. Not everyone is so thoughtful when it comes to how expensive a wedding can be for the families and friends who attend.
So sorry but you and your husband could have made the decision to not be part of the wedding party, or maybe your husband should have been the only one to stand up. So, as far as expenses, unless the future couple was aware of your financial concerns and offered to pay for some of your expenses, unfortunately, this is going to be a bit of an expense for you.
However, I'm with you on receiving a "registry suggestion" for an engagement party. Perhaps some people would think this was commomplace but, I've never seen it. A smaller, thoughtful gift, like you describe, is all I have ever done. "Registering" seems a little ridiculous UNLESS this IS their big bridal shower that they are having. Otherwise, it falls into that whole "asking for gifts" category, which I do think is rude. And... I'm with you... a nice bottle of wine with a cute card "like fine wine, may your love get better with age"... or a cute picture that you may have taken of them or of your family and them, framed, is a nice token gift. Yes, you probably have to show up with something.
Yes, I enjoy wine. Just personal message me with a $$$ amount, white, red, or what they would like and I may be able to help you.
Good luck.