The problem with these feature monsters is that you have an enormous effort to offer a file for 50 cents. That's not in any relation.
Especially since you can build a shop system directly. You only have to hire a few people for your private site to take care of it full time :-)
I look for a fancy small simply solution. But there seems to be either only such minimal solutions, which are then so cumbersome that it becomes then again a gigantic expenditure. Or you almost have to install SAP to offer a file for a small fee.
There seems to be nothing in between. At least nothing that one could afford as a private site operator.
Therefore the idea sounds very tempting, if there would come a small shopping cart, incl. PayPal integration.