Well, without knowing too much, here are a few thoughts for you. First, you probably want to hold all the money, i.e. take it from all the people first. The reason for this is you can float it while you hold it. Even if it ends up being only a couple of days, this will add up over time and enable you to take a small cut without seeming like you are taking a small cut. You can turn this into clever UI by having a screen shownig that you are waiting on these people before you can release the final payment or something like that.
Secondly, I'm pretty sure with the right processor you can credit a card for whatever amount you want, even if you haven't charged it, i.e. separate from any transaction. This depends on the processor but I think I have seen this before.
Finally, if the one person is OK with a check, that hardly costs you anything as most of the check processing system is subsidized by the federal government. Similarly, you might be able to get lower rates on incoming payments using EFT. At the same time, you can keep the cut small but you take home a higher portion because you aren't paying the credit card processor most of it.
Is this just a one time thing--or is this around a business where it is going to be happening all the time?
By processor I mean a credit card processor like Paymentech or Verisign or Cybersource. Paypal offers most processing and bank functions, but you pay for it and are forced into their API. Most of the major processors now have eCheck products, though I haven't used them and am not sure on the pricing, but it should be less than credit cards.
On the backend (you sending the one payment) I meant just doing an electronic bill pay from your bank account where they send out a paper check. This is usually free for you on a small enough scale. And it would further extend the float period.
