I got my rear tranny mount for around 125 from the dealer a year or so ago.. It is a relatively easy fix once your car is off the ground and you are able to stand underneath it, so a good mechanic should be able to do it in a minimal amount of time..
Since are legends are not getting any younger, If you haven't changed to rear tranny mount, you should have it looked at.. I didn't even know mine was busted untill I took a close look at it. It really depends on how it breaks, as to how much of a clunk or hard shift you get..
As for engine mounts, A year ago I changed the engine in my coupe but I kept the original engine mounts.. You don't usually need to change your engine mounts at all, Unless one them breaks, and believe me, you will know if one is broken