I have a 2003 HDI 90 "s" with 125k. Earlier this week the heater blower decided to pack in - perfect timing with this freezing weather

My local mechanic had a look and he said he can't find the problem, connections and fuses all fine and reccomended I take it to an auto electricians.
I've had a peruse round the boards and found a couple of similar topics - I've tried the wiggling the ignition key to check for loose connection there, still no joy.
The mechanic said theres no power getting to the motor and said it could be a relay or the unit itself. Obviously when the car is moving at a fair speed a bit of air comes through the vents and I tried changing the temp on the unit and the temp of the air does change so could it still be the unit?
So, as I've no idea when it comes to fixing virtually any problems on cars, can anyone advice roughly how much I'm looking at having to fork out at an electricians or any advice that even me as a complete doofus could possibly do myself.
Any help much appreciated

Mat