woooweeee it's a cold one here in denver today!

i noticed on my way to work this morning that the heater blower would be running fine then would slowly start to whine a little, then appear to slow in speed.  i never let it completely die, so i don't know if it actually would've stopped - before it could die i would switch it off, then back on when i just couldn't stand the cold any longer without it.

is this a common problem?  if i do need to replace the blower, is it an easy job?......and how much do they usually cost? (i've noticed some used ones on theSamba)  lastly, are there any good modifications that people are doing to the heater system that i should consider?

thanks for your help!
dusty.