RSVP and regrets only

Having everyone RSVP online doesn't cost more than having just declines RSVP online.

So if people don't respond you will assume they are coming. You won't know if people didn't respond because they forgot (or the invitation was lost) and don't plan on coming. You could end of paying for meals of guests who don't end up coming. You should have everyone RSVP online.

I think this is a great way to potentially waste money.

If people's invite gets lost in the mail, they forget to RSVP, they have issues with the website, etc. you will still be paying for them. I feel pretty certain that your per plate cost is going to be more than sending a standard RSVP card with a stamped envelope.

Explain how this will save money?

I should have clarified. I'm actually asking if it is appropriate to have people RSVP through our website instead of sending out rsvp cards/return postage.

RSVP online is fine, but you want everyone to respond, those who can come and those who can't. You'll get the most accurate headcount that way.

If you feel that all of your guests are computer savvy, I think online RSVPs are fine.

Online RSVPs are fine.

The guest can decline online as well. You should want to have a clear decision for everyone you invite. I would have everyone go to the RSVP page and accept or decline the invitation.

Of all the places to spend money?

This is the place to spend a little. Make it as easy as your guests to reply.

ETD; most people here are paying for all or part of their wedding.

Online is fine. I did it via the knot. You can also list meal preference there. I still had to follow up just as much as people seem to with paper invites though but I didn't waste stamps.

As PPs said, have everyone accept or decline.