If guests did not ask to be invited, then why should they be asked to pay just so the couple can have a lavish wedding? For that, I can go out to an elegant restaurant of my choice.

If the couple cannot afford a lavish wedding party, then they should either opt for something affordable, or save up. Guests are the ones they chose to invite. It's like telling them, if you want to come, you have to pay.

I would however give a giftcard so they can buy what they need but that's my choice.

If anyone ever invited me but told me I had to pay, I would definitely decline and just wish the couple well.