AFIAK they dont charge you to recieve money, but they do charge to get it from PP to your bank account. However, if like me, you live on eBay, you can use the money to pay for items on there instead. Depends on how many people want to pay with PP.
Saying that, I just had a quick look on PP and its free for £50.00 GBP or more, £0.25 GBP for £49.99 GBP or less, so just wait for everyone to pay and transfer it then I guess