Pay per download

Hello

I created a blog for a client who runs a record label. people used to pay with paypal and then he’d ship a CD. now he would like people to be able to download directly from the site. is there a plugin for wordpress that can do this?

I’ve searched on the web and I can’t see much, so I am guessing that in order to be able to do this I would need some kind of a hack. So I would appreciate any help pointing me in the right direction for this sort of info as I don’t mind making something, I’m just not sure where to start.

Thanks