you can price the tires on www.tirerack.com, you will
pay UPS, then you will have to pay someone to install them. or you could price them at a wholesale club, like
Sam's or Costco. much depends on comparing available brands to fit your vehicle. run flats are not cheap
You are right about how hard to find run flats. Most tire shop won't sell them. I think one of the biggest reason for this is because most of them gets really noisy within the warranty period. I have seen many vehicle owner who just replace them with good quality tires and either keep a donut spare tire in the trunk or few cans of "Fix a Flat".