here in Tampa there's a place that sells used tires, including name brand summer tires. It's not unusual to see good tires with 60 plus pct of tread left to be advertised for around 1/3 of what TireRack will sell them for. Oh btw this place's price includes mounting and balancing. They also seem to advertise lots of runflats and they are advertised even cheaper.
Like you, there are many people thinking about ditching their OEM wheels and tires to replace with aftermarket. I think the market price for 161s is probably around 250 to 300 for a complete set, depending on condition.
From what I've seen, prices for other cars' wheels are even cheaper. At least some people want OEM BMW wheels.