They make good mics but their quality control is not so amazing. A good audio shop will let you test the mic out before you buy it so you get a good copy.
A great place to get amazing info on bargain mics is over at dvxuser.com in the audio forum.
Also any mic will sound so much better if you use a small portable mixer instead of the preamps on your camera.
For budget mics I always loved AKG Blueline. They are used by the big audio guys in movies where they are worried about damaging their really expensive Schoeps and Sennheisers. This hypercardiod sounds really amazing for the price.
http://www.bhphotovideo.com/c/produc...icrophone.html