There are some other driving schools and/or open lapping companies that run events at Mosport.
However, they don't generally allow someone who has little driving experience (Trackmasters for example...).
The BMW Club membership is only about $50 per year, and you get a few other benefits as well. We run Auto-X events once a month, along with a Go-Karting series that starts Jan 7th.
As to whether or not it's worth it....you must be kidding. I wouldn't miss it for the world. In fact, a few of us are planning a January trip to Sebring for the school / club race down there.
I'm not sure I can wait the four months until April....
I'm not really an asshole, I just play one on the Internet