If you want merino wool underwear for a reasonable price then try these sites:
This site sells NZ merino wool only. Also, they sell only a unisex style:
http://www.faxmail.co.nz/mavlin/
This site sells Australian merino wool only. They have separate mens and womens and more of a size range:
http://www.wool-underwear.com/
This site is a US retailer and they sell only Australian merino wool:
http://www.vermontcountrystore.com/shopping/product/detailmain.jsp?itemID=29395&itemType=PRODUCT&iProductID=29395
I have tops and bottoms from both the first and second site. I have worn both. The quality of both is excellant. I have a slight, very slight, preference for the NZ merino.
I have never worn a merino/synthetic blend and don't think I ever would. Why degrade the merino by blending with a synthetic? Maybe price, but at the price these 3 are selling at, that is not necessary.
You do not have to pay the Smartwool, Ibex or Icebreaker prices to get quality merino wool underwear. Maybe if they get some real competition, then they will lower their prices.
I am NOT affilated with any of the above other than being a customer of all 3.