How much could I expect to pay to replace my timing chain/tensioner on my 94 325i? Private mech or dealer?

I am pretty sure your engine is interference in which case you most likely have bent valves which equals an expensive repair bill. Dealers are outrageous so look for a good independent Beemer shop.

Roughly, how expensive are we talking?

I can't say because I don't know the extent of the damage. Do your homework and find a good local BMW specialist.

Depending on extend of damage ur talking from 2,500 to 5,000, just to give u an idea