I'm not sure if this has been discussed for sure but the Goodwill is a great source for Merino and Merino blended sweaters and sometimes shirts. I found a mens mid weight sweater, heavy weight sweater and numerous womans shirts/sweaters with 100% Merino. I have found some Merino blends that are 88/12 merino/nylon and one 80/20 merino/poly. My girlfriend found an Icebreaker tank top that retails $45 that she uses as her regular trail running shirt. Not to mention the other numerous TNF and Columbia Fleeces/Jackets that are lurking around there sometimes (but who needs that? :P)
I make gloves, socks, beanies, and headbands out of the womans shirts and sweaters I find as they are generally "Extra-fine" and very nice on bare skin. The sweaters are nice to layer with a merino baselayer.
Just a heads up for the budget backpacker and MYOGer.
Sorry for my long-winded nature.