Topsky makes a really nice airplane. You can expect pretty impressive performance. Given that the bare airframe weighs less than 80 g, it is unquestionably going to fly rings around the Libelle. Obviously your $120 or whatever only gets you the airframe. You still need the tiny servos and the like. Which is where I'll recommend going as light as you can on R/C equipment. The little HK 1.9 g servos will work fine and are sufficiently light, though you may need to require the connectors. I believe there's an Orange receiver that fits them as-is, but don't quote me on that. Regardless, the smaller Orange receivers are what you'd want. It'll only need a little 1s Lipo, although some of those units will run on 2s as well. I fly my small DLG on a 150 mah 2s, mainly to get some nose weight way up front.
The Libelle is a nice airplane, but don't expect contest performance. It will handle nicely in wind, and being bigger, is easier to see. That also means it crashes harder, and I can't give a comparison as to the robustness of the two airframes since I've not flown either myself. They are both very reputable products.
If you're looking to really go budget, the HK .9 m mini DLG is supposed to be a pretty good buy. It won't perform quite as well as the Topsky, but it will thermal. Its only real vice is that the area where the boom attaches to the pod is prone to cracking. Just put glass cloth on there when (not if) it does.
A little higher up the price index is the Binary DLG. It's supposed to be a very good product as well, probably comparable to the Topsky.
Obviously this tends to push toward the Topsky. Hey, they make airplanes for competition, and they win. That says a lot right there. My one complaint with the Super Mini is that the control rods are run on the outside of the boom. I've never liked that stuff out in the wind. It just adds drag. I've saved a good deal of weight using lighter pushrods run through the tailboom. If you have spring actuated tail surfaces, you can cut those rods down to .020 piano wire, at which point they weigh a couple grams at most. I think they're also recommending larger servos than I'd use, simply because I'm not asking for that lightning response--I don't fly competition, and I haven't seen where faster servos really improve my flying. A major goal, after all, of soaring, is to use as little control input as possible so as to reduce maneuvering drag which kills altitude.
