Firstly, I am no skimmer expert, this is only from my own (limited) experience and quite a bit of reading. There are some skimmers that the reviews indicate perform pretty well for a modest price e.g. the Bubble Magus, having said that it seems they aren't as cheap as they apparently once were. My honest advice on skimmers is that it's one area where you really do not want to cheap out.
I did, (it's made by Weipro) and even after a year of fiddling with the thing I'm still bitterly regretting it. Thank goodness I'm only FOWLR and on a 27 gallon frequent water changes are cheap. OK it was only about $80 ($80 absolutely wasted), but it is the biggest piece of junk that ever showed it's miserable face on Earth. I literally despise the thing. I can't wait to get my new tank running so I can drive a steamroller over it. Repeatedly. It's sole purpose is now aeration, because I could do a better job of skimming myself with a drinking straw and a spoon..
With an upgrade in progress I've done a lot of research, and from what I've read you'll probably be best off looking towards the Vertex/Euro Reef price range as an entry point (though there do seem to be some questions on the Euro Reef meshwheels at present).
My tank upgrade has a Euro Reef RS100 (pinwheel) waiting, just to show I've learned my lesson!
