We have a Trane furnace that's 90% efficient. It's probably 7-10 years old. It is making a buzzinng sound when the blower comes on for the air conditioning so the ac guy said it needed a new blower and maybe new bearings. If the unit is on the older side - he said it would be around 1000.00 to fix, is it worth putting that into the unit or should we get a new one? Also, is a blower hard to replace on our own? I've seen that blowers cost about 125.00 on the internet.

May just be the Capacitor, I would test and/or replace.
With power off, I would see if blower spins freely.