There's no single price, because a buyer running a $2M/month account and a buyer taking on a scoped one-time project aren't the same job. Rates are set per engagement, and you see the number before you commit to anything.
What the rate depends on
The type of engagement, the scale you're operating at, and how much of the buyer's week the work takes. A senior operator in your account daily costs more than a monthly advisory call, and it should.
What's included in the rate
The marketplace fee is already inside the rate you see. It isn't added on top as a separate line, and there's no card or processing fee on your payment. The number you agree to is the number you pay.
When you see the number
Before you commit. You're matched with buyers, you talk to them about scope, and the rate for that scope is what appears on the platform. Nothing gets charged before you agree to it.
Budgeting beyond the buyer
The rate covers the buyer. Your ad spend, creative production, and tooling sit outside it. Worth separating those in your head when you're deciding what you can commit to.