I have a pair of B&W 801 Matrix 2. One of the crossovers burnt out. What am I to do?

Plenty of good advice thus far.  I hope you find a reasonably priced and easy fix.  

Also would help to see your system listed so we can know and admire what kind of ungodly current you've been feeding those 801's to fry the crossover/tweeter, etc. Must have been a rager of a party!