The blower motor is difficult to get to - you have to completely remove the upper half of the dash - not a simple job, hence the $650.00
Suggest you have a dealer confirm that he agrees that it is a blower motor before proceeding.
It is possible that something has gotten past the cabin air filter and into the chamber behind the firewall where the blower wheels are located - anything caught there might be rubbing on the edge of one of the blower cages - need to remove the intake air ducts at the firewall and inspect.
'99 BMW 540i6 (black on black)
'99 Lexus Rx300