I own three BMW's bought in Vancouver, BC. For 23K Canadian you can get a used E46 (3 series) or a used E39 (5 series). I bought a used 528i in your price range. Note to Americans, Bimmers are more expensive in Canada (exchange rate).
If you're a young guy, you'll probably want the three, if you are older and tired of being cramped in Jap cars most of your life, you'll love the five. Both the five and the three are great cars. I own a 318i, 330xi and a 528i; my favourite car is the five.
I've helped guys buy Bimmers who live in different provinces but don't have a great selection of what you want. Brian Jessel in Vancouver ( a dealer) sells the most Bimmers a month than any other Canuck dealership. They also have the largest used stock on hand in Canada.
There are two philosophies out there: 1) never buy used from the dealership, you'll pay too much 2) only buy from the dealership, chances are you will get a better car. I'm in the second category.
A true story: I bought the 318i (1994 with 82,000 Kilometres) from Jessel a couple of months ago. I drove it off the lot; two days latter I had pulsing in my electrical; a new alternator was installed - no arguement from the dealer. About a month and a half latter, the starter gave me problems, a new starter was installed, no arguements given from the dealer - in fact, my salesman was insistent it be fixed by them. Can you imagine what would have happened if this had been a private purchase? Also, purchasing through the dealer is best if the car has a history of being repaired by them, they have all the records and give you the low down on the car up keep.
You can actually become good at reading "into" the maintance history of a car. For example, if a guy rotates his tires every year, you know you're buying a car that was maintained by a Bimmer fanatic - most guys won't rotate their tires to save money.