Short answer: online RSVPs cost nothing on most wedding sites, including ours. What you pay for, if anything, is what sits around the RSVP: the website, the design templates, and the fees on gifts. Here is how each of the common options actually charges, so the phrase "free RSVP" on a homepage does not surprise you later.
What online RSVPs cost on the big wedding sites
The Knot, Zola, and Joy all include online RSVP with a free wedding website. Guests open the site, find their name, and reply. None of them charge per RSVP. Where money changes hands is elsewhere: paid design upgrades, custom domains at $20 to $40 a year, and, on the ones with cash funds, a fee taken from each gift a guest gives, sometimes with a "tip the platform" line shown to the guest at checkout.
What paper RSVPs cost
A printed RSVP card with a stamped return envelope runs $1 to $3 per guest once you add printing and two stamps. For 120 guests that is $120 to $360, plus the weeks of waiting and the chasing that follows. Even with online RSVPs, only about 80 percent of guests have replied eight weeks after the invitation goes out (RSVPify). Paper adds the mail on top.
What the RSVP costs on TheWeddingTicket
Nothing, and there is no upgrade tier behind it. The invitation goes out by text or email, the guest taps once to reply, picks a meal, and can give a gift toward the wedding in the same tap if they want to. No cost for couples. When a guest chooses to give, there is a small processing fee, shown clearly at checkout. Nothing about your wedding is published or searchable; the invitation reaches guests only through the link you send.
The question behind the question
Couples searching for the cost of online RSVPs are usually really asking whether guests will actually use them. They will, if the RSVP arrives on their phone and takes one tap, with no account to create. Paper takes weeks. A website that makes guests create an account takes forever.
See a sample invitation the way a guest would, RSVP and all. And if the bigger question is how to pay for the whole wedding, that page is here.