Why is Dragon Medical and Legal so expensive?!?

Is there a cheaper alternative that is similar in quality??

You get what you pay for...remember "buy cheap, buy twice".

They are specialized programs, and since these sectors can pay for it, the price reflects that.  That said, if you don't want the functionality and particuarly the vocabulary of the legal/medical editions, from what I understand all the functional bonuses (like macros and advanced scripting) are available cheaper if you simply buy dragon pro.