on the cheap, you really want to watch out for cr@p trems.
here's my list of the good ones, with some more info (nicked from UG, lol- don't worry, i wrote it, i'm not plagiarising anyone, lol):
"Cheap double locking trems are more bother than they’re worth. They’re made of cr@p soft metal, they won’t hold tune and they won‘t sustain as well. You MAY get lucky, but it’s not worth the risk. Either fork out for a good trem (Original Floyd Rose, Floyd Rose Pro, Floyd Rose Speedloader, Schaller, Gotoh, Kahler or Ibanez Edge (NOT Edge III), Ibanez Lo-Pro Edge, Ibanez Edge Pro (NOT Edge Pro II), or Ibanez ZR, and most expensive guitar brands’ own brand of trem (e.g. Vigier) - if it’s not one of these, assume it’s cr@p, unless proven otherwise), or go with a hardtail or non-locking trem. Also, a lot of the decent trems are a different size to the cr@p ones (even the studs can be a different size, if the whole trem is the same size) so it’s frequently not just a matter of buying a better trem when your cr@p one breaks. Most guitar companies are incredibly scabby- they’re TRYING to make it hard to upgrade, so you have to buy a whole new guitar from them."
so yeah, that's about the best advice i can give.
