Mitsubishi parts in my area cost brand new regulators around these prices from memory:
New front window reg $170-180ish
New Rear window reg $140-150ish
No need to get another motor - you can easily test it by separating it from the regulator and test it (itll be right)
In my opinion dont waste your money on a second hand regulator. Whether it be $80 or whatever they are second hand, its dead money.
Brand new ones from Mitsubishi are now a revised unit which contains a support brace which braces the area which snaps on the regulators (which cause your problem to begin with)
Take it from me, second hand regulators wont take long to fk up
my 2c