Escrow api/Kickstarter/Upwork/Fiverr

Hey guys,

I’m working with a small team on a ministry app. And I’m lost on what is the best way to implement a escrow/payment gateway.

Here’s how it currently works.

There are two users.
I) Sponsor
II) Participant

Sponsor invites Partcipant to complete a task.

(Sponsor pays upfront).

Participant can see money has been “put up” and is available to them, if they complete the assigned task.

Once assigned task is completed. Admin is notified, to verify completion, and the money is released/transferred to the Participant.

Is what I’m looking for an Escrow?
There are several other notable companies who do these types of transactions; Kickstarter, Fiverr, Upwork. I’m just looking for the best value solution.

E.g.,I looked at the Escrow Api and it’s $10 for $100 transaction, which seems steep.

I’d appreciate any useful advice!