There's no reason why a shop couldn't be setup strictly DIY either. It's just a question of looking into the economics to figure out how much you can charge for mp3 and how economical it would be. The costs would essentially be bandwidth, space, service charges for credit cards. The bandwidth and server space issues are easy enough to deal with since the cataloging of files can be distributed over different servers on the net which would be invisible to an end user. Since the style of music here is largely a labor of love for many computer geeks, it's possible that you'd find a good number of people that would give out server space for next to nothing if not free, or for the ability to legally play the songs on their server in their home. If you use something like paypal, from the quick look I've done, they charge about 3% per transaction plus a $0.30 transaction fee. So, the question from there would just be figuring out an implementation that would make it affordable. Itunes sells tracks for $0.99.
You could be competitive with using something like paypal through using a points system where people purchase X number of downloads in one shot to keep the $0.30 paypal transaction fee from eating into costs too much. Then, there is also the option of selling your music through already existing services as well like Itunes. Ihave not found what the exact cost break down is for Itunes as far as payment is concerned. But, one advantage they do offer is that they will hit up that Ipod market and there is DRM in their formats for people who are concerned. Hell, one could always take advantage of both. Those are just two means I thought about this morning. There are likely more. Honestly, I think the hardest thing would be the same as the past, letting people know that your music exists. And there is no reason why, in the process of going the digital route, one would need to stop cutting vinyl either.