I'm another very happy eMusic subscriber. I've been using eMu for 3 years now. I was grandfathered in to an old subscription rate about 2 years ago, so I pay 22 cents a track, but the current equivalent subscription rate is 25 cents a track. That's still very low, and I don't know of any other legal download site that has such a low price. (Or even lower than 40 cents a track, for that matter.) One thing to consider is that while many people start out with a basic eMu plan, which is more expensive per track, once they've been on the service a while and found they like it, they often upgrade to a plan with a lower per track rate.

There is a huge amount of Irish, Scottish, and English music on eMusic. There's also music from Wales and Brittany and more if you're willing to give other things a try. There's plenty of the traditional folk music you seem to be describing. It is subscription only though, which might not work for people who just want to download on an occasional basis. However, they've recently added quarterly plans along with the monthly and annual plans, and that may appeal more to some people. (I think the deal is you pay once during the quarter, and then get 90 days to download your tracks.) You can lisen to 30 second samples on eMu.

When eMu doesn't have a recording, other sources I've used for downloading are Amazon.com and cdbaby.com. You can also hear samples on these sites. And Compass records, which has a lot of Celtic recordings, has just started making downloads available.