If you’re based in the US, Weebly won’t charge any transaction fees. But if you are using an external payment gateway (e.g. Stripe or Paypal) you’ll pay a fee to them. They both currently charge 2,9 % + 0,30 US$ per transaction.
Outside of the US, you’ll be charged a 3% transaction fee if you’re on the Weebly Pro plan, on top of any payment processing fees.