the variable speed motor on my AC unit went out and it is very expensive to replace. I was told I could convert to a fan with a relay, which is much cheapers. What are the pros and cons of doing this and is it recommended?

I can't see anything wrong with it right off the bat. I also can't see why it wouldn't work fine. Your new fixed blower motor probably will have 2 or 3 speed taps so you could in theory adjust the motor speed, say if you were getting too much humidiity or a lot of static electricity.

I suppose he plans on pulling the control board and putting in a standard relay. That would work. I know the low voltage fuse is usually on the control board on those variable speed motors so make sure to ask that they wire one into the system somewhere.

Im not sure Im understanding this completley. You say the motor is bad. So if the control board is fine, there should be no need for an extra relay. And what do you mean by "fan"? Did they suggest just using a fan in stead of a blower motor assembly? Please give much more detail about what was suggested to you. Doesn't compute to me at this point. I see know reason you couldn't get a cheaper universal motor to replace the spendy one that come with the unit as long as it meets the specs of the original one. Then you would just have to wire it correctly to the baord, which already has the fan relay and control built in.