I can confirm that it is a pretty substantial undertaking to replace the blower motor, mainly due to the "buried" location and enclosed access to the blower plenum compartment.
Like many modern vehicles, the first item placed on the assembly line appears to be the HVAC unit, then they build a car around it

. Just for good measure, the HVAC assembly is behind the dash frame rail tubing, which also hampers access and therefore has to be dismounted (it's a bolt on) to allow the numerous ducts to be removed from their lodgings, unharmed.
Whoever is giving you those prices needs to be asked this simple question:
When was the last time you replaced a blower motor on a 2012 L322?
Although the 2006-2009 models look very similar to the final update of the L322 model (2010-2012) "behind the scenes" these models are significantly different from the earlier edition.
It's not the end of the world if none of them have but it is an advantage if one of the vendors has carried out this work previously on a 2010-12.
The main body harness is completely different and runs across and behind the dash in a toughened plastic cavity. The "tributaries" that branch off it have specific clips and mounts which, if not refitted exactly as they left Solihull, will produce various irritating rattles and clicks behind the dash.
The main fusebox and body control is now co-located behind the lower glovebox.
The process is quite straightforward BUT there are multiple connectors which will need to be unplugged and reconnected, including multiple yellow SRS connectors.
Once the job is complete, before you accept the return of the car, make sure you test the car thoroughly to ensure that all the various switches, buttons, knobs, controls, security system, ICE and upper and lower glovebox releases etc work correctly.
FWIW, a common cause of blower bearing failures (across various makes and models) is the lack of regular cabin filter replacement.
You may want to check your cabin filter - under the hood, at the foot of the windshield cowl, in a horizontal cavity with the retainer cover held in place by four clips at the lower edge.
Rob