even in Canada there are many E60s for sale - especially the 2006 year. A lot were produced back in the day. Supply and demand. Almost everyone who wants one, already owns one. And, there is no true price discovery - prices ARE all over the map ranging from CAD$15K to $38K. There does seem to be some correlation with mileage.
I count about 30 2006 M5 / M6s for sale on kijiji.ca for all of Canada - that's about the equivalent of 300 for sale in the USA. M6s seem to be slightly more expensive for equivalent mileage, but that may just be the "dealer" factor. If I expand the search to be 2006 - 2010, there are about 65 M5s and M6s for sale. That's a lot. There are zero E39 M5s for sale in Canada right now on Kijiji.
Some data from the 2006s:
> 125K kms = CAD$20K or less.
90K - 125K kms = CAD$20K - $25K
There are outliers, probably based on regional supply / demand.
62K kms = CAD$38K (one car)
65.7K kms = CAD$32.8K (one car)
130K kms = CAD$30K (one car)
I paid around CAD$29K for mine with 105K kms but it had an Eisenmann Race exhaust, HR race springs, front and back HartGE spoiler / diffuser, and Radenergie R10 20 inch rims. Selling the exhaust (has the original) and the original wheels (kept the R10s of course) reduced the price by about CAD$4.5K - so $25K for 105K kms. Don't forget that in most regions there is a 13% tax on car sales (even used ones).
Here is the link to the kijiji search for 2006 M5s and M6s