I recently bought a refractometer on ebay for about $30 shipped. Mostly aluminum, came with a hard-shell case with foam liner, pipette and adjustment screwdriver. It seems to work just fine, and seems more than rugged enough (especially compared to what I was using before - a fragile glass hydrometer); I'm not disappointed with its quality.
I'm no expert on its use, but the beersmith software I use has a refractometer tool that can do all the work: converting OG reading in brix to specific gravity, converting a fermented wort reading to SG (using the current brix reading as well as an OG reading), calculating an accurate ABV and predicting the OG of a finished beer, and dealing with the maltose correction factor.
If you have software that can do that stuff, a refractometer is really handy. If not, there are probably free online tools, or if you're into programming you could throw something together yourself. I wouldn't want to have to do all those calculations out by hand each time though