You definitely get what you pay for. I have been looking for close to 4 months and it is hard to find something that is genuinely nice. There are lots to chose from our there in the US, but Canada can get tricky. You also have to contend with rust up here too. Watch out for the rear of the rear of the wheel arches, two spots on the body at the base of the trunklid and jacking points. Bring a magnet with you!!
Add to that you now also have US buyers coming across the border with the exchange rate engine what it is (15k CDN = 12k US right now). Prices seem to be going up with the nice weather coming.
I would say 15k is a reasonable budget, but you still may have to do some fix it items. It will be hard to find a 2001+ for under this with under 160k km and well cared for. Seems high I know - but the fix-up costs add up quick (keys cost $250 alone FYI). For under 15k, you may have to search for a 2000. If you want cheaper than that you will have to move very fast once something cames up. There was a 2003 $6500 one in Cambridge back in Nov and trust me you won't want to see what that gets you! I made out really well as I bought on the coldest day of the year and came in with an offer at the ideal time when the owner had it off the market for the winter and I kept in touch. Car has some issues that I can fix but may have turned some people away (clutch slips like crazy etc).
If you find one - pull a Ontario used vehicle report for $20 at the ministry (this would have helped with the Sarnia one) and call the owners if you can find them (google and 411.ca are great for this). I called the previous owners on mine and learned everything I ever wanted to know about the car and then some. The previous owner owned the car for 8 years and only pushed the Sport button under a dozen times as he was scared of it. I pressed it that many times on my way home
From what I have read, there were just under 700 E39 M5's sold in Canada - good luck in finding one of them. If I see anything on kijiji or Autotrader I will let you now through here.
Here is some inspiration for you. This is how my car looked on day 1 after passing the Driveclean test finally last week before going into winter hibernation (had to update software at Canadian Tire to get it to read). Needs a good cleaning as it has been sitting for a while.. but will clean up very nice. 100% original not a single mod. Bring on the nice weather!!