Brands that I would recommend:
The last two are fairly new, both produced by people that care. In fact, Fortaleza refuses to increase production, even though the demand is high, as they don't want quality to suffer. I haven't had the ocho, but have constantly heard good things about it.
Most of the new expensive brands on the market should be avoided. They're just marketing-crazed inferior products like vodka. If are a lot of decent cheap 100% agave brands out there under $30, but they are brands you have never heard of before. But they are not all good, so try to stick to those you have never heard of.
Lastly, in my opinion, old classics like Herradura, Chinaco, Gran Centenario, and Don Julio have pushed production to such a degree that the quality is inconsistent and I wouldn't trust picking up a bottle of any of these.