I should probably quit commenting because I don't intend to get a spare, at least before I have a problem it would have helped with, but I have one more comment. I you want to save some money, the bmw jack doesn't look special at all to me. You can buy a simple jack like that for about $30. Here is a link to an example:
http://www.amazon.com/Scissor-Jack-T...=pd_sbs_auto_5
I would weld a piece of retangular steel tubing 1 inch square to fit the lifting pockets of the 1 to the top. You could get a wheel cock if you want it but all you need to do is set the brake or put the car in gear or both. You need a wrench for the wheel bolts but I have those in the car already. I like an extendable 3/8 ratchet and a deep well 17mm socket. If you want a torque wrench, you can get one for less than $20 from Harbor Freight.
My point is just that you can get by spending a lot less than $100 on a jack setup. It will not be as nice but should work just fine. I wouldn't be cheap on the wheel and tire but simple jacks like this won't work a lot of times but for a few times, you don't need anything fancy. You could wear one out but you almost certainly won't.
Jim