Leanpub accepts standard Markdown (though does have its own markdown format now) and gives you an "export for printing" button that you can upload to Lulu. The cover was kind of tricky and I got some professional design help both to design it and to get the margins and bleeds exactly as Lulu wanted them, but the result was way better than I expected.
I haven't tried the other professional tools mentioned in this article so I can't really compare quality or ease, but might be worth a look if anyone is looking for something in between "do it all yourself" and "pay for fancy tools". (I have a lifetime LeanPub license from back when they still offered them but the monthly subscription fees are a lot lower than some of the tools mentioned here and you can easily get a printing done in a single month).