A few months ago my cabin fan started to loose speed and stop blowing air after 20-30 seconds of operation. I pulled it out, cleaned it of all the dust, pulled it apart, oiled the bearings (brushes not ball bearings) and reassembled it.
Works as good as new.

 

I think you can probably fix 70% of the blower motor fails by cleaning, oiling, cleaning the commutator, and replacing brushes. It could be 3 hours of your time though.

I would be very scared of a ebay blower motor. Go with a reputable supplier for after market or OE new, or rebuild. I used part, you will be in the same boat you are in now.

 

When these fans fail it's usually either not spinning at all, or it gets loud from loose bearings- neither of which sound like they fit your situation. If you're just getting low air flow, I'll bet it's not your fan at all, but an airflow obstruction somewhere- most likely in the cabin air filter. If turning on recirculate fixes the airflow issue, then it is at the intake point under the cowl.

I wouldn't trust an aftermarket blower fan unless it was a name brand with a good reputation- a new German one like a Nissens or VDO will run you about $140 if you have a T1/T2. If you have to go cheap, I'd probably do used ones and add a bit of fresh oil to the bearings as they are really quick and easy to swap out.

 

I ended up with a used fan off Ebay. The changeout when very smoothly and a month later, still loads of cold air in my tropical heat. Cost me $60. plus $30 for my mechanic to change it. Labour is cheap down island way!