I think your best bet will be to first call around for the best price on the motor, then call around for best price to install.
Typically I pay $60-$125 for a motor - and if I'm in a rush and have to have it installed, I'll pay $125-$200 to have it installed. So a quote of $700 either means that you're getting gouged or
that the way yours is set up makes it a very tough job.
Sometimes they can be very tricky. There are hundreds of different motors mounted dozens of different ways. But since yours has to come out anyway, it can't hurt to take a closer look.
** Be sure the motor is an exact match with yours. You probably won't find that exact model, so all the other details (amps, spin direction, shaft size [both length and
diameter, mount holes, etc.) have to match. Write down everything from the metal tag on the motor (you may need to squeeze in there to see it). You won't find the motor at Lowe's or Home depot; you'll be calling HVAC suppliers that you've probably never visited.
** Scour your paperwork, and Comfortmaker's site
for anything that will help diagram-wise.
Can't hurt, too, to call where you got it to see if they've got instructions. It will be your best - and probably only - source for a step-by-step.
Generally, look for these issues:
** Shut off the breaker.
** Can you see where and how the motor's "feet" are mounted? Sometimes it's mounted to the "floor" of the furnace, but other times it's mounted to a "rack" that slides out. You'll hope yours is that way. If it is, then locate the couple of screws or bolts that you can remove to slide it - with the motor - out.
** Can you see how to remove the fan from the driveshaft? Or if you have a "squirrel cage" (a round turbine looking type of fan), can you see how it's mounted?
Yes, sounds simple - but sometimes it's not. Study where and how it's all mounted very carefully.
If you can easily see these things - and are sure you can get to it all, and have the right tools
- disconnect the wires and start removing screws and/or bolts one at a time.
Once the motor's out, remove the fan or squirrel cage.
Now it's a matter of all in reverse to get the new motor in.
I hope this at least helps a bit.