They seem to be all over as you say.
Some enthusiasts think that their well maintained M sports are worth their weight in gold, then you have the ones that were owned by random people who just drove them and didn't go beyond basic maintenance that are selling them for much more reasonable/cheap(ish) price.
Neither group is wrong.
Focus on the car, the condition, the seller and then look at the price which is relative to the rest of the car.
Paying a grand or two more for a well sorted one is worth more than saving a grand or two to spend it in a while.
www.enthusiastauto.caNeed a car???
--'00 BMW ///M5 .:Jet BLK/BLK:. Individual-1 of 1 - Style 65 Wheels; 9.5" Square Set up;275 Tires;10mm/3mm Spacers; Black Kidneys;Muffler Delete; 3.5" Dual Tips; Beast Power; "Dinan" Ducts; E60 SSK; BC Coils
--'04 Volvo S60R/6spd.:Nautical Blue/Gobi&Black
'00 BMW ///M5 .:Avus Blue/Grey/Black:. 1 of 8 SOLD
'88 BMW 635CSi Blue/Tan Sport
'81 MB 500 SEC Euro Koenig