A.D., you're kind of asking the wrong guy... I'm just a hobbyist and I have a top-of-the-line DMM. I have a thing for excellent tools.
But if I had to buy the least-expensive practical DMM I could buy, I might buy this one:
http://www.multimeterwarehouse.com/m838f.htmThe reason I selected it is that it apparently offers temperature reading as well, which as an espresso machine owner you might find useful. Disclaimer, though, I have just looked very quickly at that site and this device. They do have many, many other products there, and moving up the ladder gets you features of convenience and capability you might possibly want some day, for only $20-$30 more.
EDIT: The least-expensive Radio Shack models are analog meters that aren't usually as fast-acting, versatile, or long-term reliable as digitals. If you want to buy from them for some reason, this might be the best bet but it has no temperature capability:
http://www.radioshack.com/product/index...Id=2103176But, as I said, I'm not the guy you should be asking for advice about inexpensive tools.

I could quickly take you into the $150 range, or even the $800 range like mine, but the function you need for this test A.D. is about the most common and most basic function of a DMM. You could buy or borrow pretty much ANY working DMM and be able to test resistance with it.
Good luck.