I was just in the same dilemma last week, except I just cut my yard, once a week. But I like to have good stuff. I just started looking on Craigslist and ebay, and a western NC classified site. When I found something I would look it up and learn about it. I wanted a 2 stroke with a straight shaft, and basically narrowed it down to a Stihl FS80 or FS85, or a Shindaiwa, Dolmar, Redmax or Tanaka unit. Since nobody around here knows what those are, they don't own them, so I couldn't find any used.
I ended up finding a Stihl FS85 for $125. Called the guy and talked to him, he said come get it for $100. When I got there, he threw in a Homelite weedeater and a hedge trimmer attachment for the Stihl, and took $80 bucks for it. I did have to replace the throttle cable for $20, but other than that, it cranks and runs like a champ! I spent about 45 minutes with it this past weekend and it beats the heck out of my dad's Ryobi 4 stroke and my old Homelite 2 stroke.
Hope thats helpful. The 2 stroke is a good bit lighter, and has a lot more power than the 4 strokes that I have used. Mixing fuel isn't a big deal, make it a gallon or more at a time. I used about 1/3 tank in the 45 minutes that I was running mine.