It depends on what sort of cleaver you want.
Chinese cleavers, which really are rectangular bladed knives, I'd spend about what I'd spend on a knife, taking into account how often you'll use it.
True cleavers then come in a bit of a variety.
You basic cleaver, the one you see in all the cartoons, you want a solid bit of steel and you're not worried about the edge so I wouldn't go too expensive. A Henckels would be perfect.
If you want a heavy duty cleaver, then shop around. You'll need to do some research into just how big you want to go. Quite often they have unusual shapes designed to increase the mass of the blade. Something like this one has three pounds of bone crushing goodness.
In my book the apex of cleaverdom is the French sheet cleaver, aka swiss cleaver aka feuille droit. It has a sharp edge and a blade that curves up to a tip so it can do cutting work which is great for removing tendonds and gristle, but it also has the heft of a big cleaver.
Linky to an example: