True, but imagine being stranded in the woods with your kids in the car. Or in the middle of the night on the highway. I can give you countless reasons of why $200 is a small price to pay to be on four wheels again.
On the other hand, I don't trust the slime thingy.

I've used the slime on a Grand Cherokee with TPMS. I was charged $20 to clean out the tire and clean off the TPMS sensor. The sensor didn't report properly when I had it in there but after it was cleaned out, it worked fine until I sold the vehicle a year and a half later.

Heck, even BMW offers a kit that uses sealant:
ShopBMWUSA.com: BMW MOBILITY KIT

The sealant is also water soluble.

Perhaps years ago you didn't want to use these products but there really isn't a problem anymore. If you really want buy the BMW version and if your TPMS sensor gets killed (it won't) then ask BMW to replace it.

With any tire, IMHO, this stuff should only be used to get you out of a situation and to a tire shop - not as a fix.

^^^Correct. Most tire sealants on sale today are advertised as TPS safe.
I tow a lot and my X5 didnt come with a spare. I was having the trailer spare in the spot for the space saver-they are the same size. But in case i have a trailer hooked-up I cannot use the tiny spare tire in the back. So I was sticking with the runflats for a long time and having a full size spare in the trunk for this occasions. Until I forgot it once and I destroyed a tire in the middle of nowhere. So now I have space saver spare(it is from E53 with 20" wheels, I just grinded the center bore bit), mobility kit and a full size spare for a long tows. I have to make a brackets for the spares on both trailers.
I went with Toyo Proxes ST2 and I am pleased with them. Ride quality is good, noise is Ok, but i feel their wet performance may be not on par with Bridgestone RFTs. Bridgestones were good for less than 15 k miles on the rear(with minimum camber setting) hope that Toyos will make at least double that for half the price.

I have Michilins on the X5 now but will switch to Contis (DWS) as soon as the Mich's are worn a bit more. I've used Contis on my e53 for 4 years and they perform well in all respects, plus they really are great in snow (even deep snow).

For the OP, the answer depends in part on whether you need snows/winters, can get by with all seasons (as I can), or live the luxurious life of summer tires year-round. No matter the tire options, I never scrimp on tires or brakes, two areas where a few bucks saved could result in a serious accident. I don't run my tires down to the wear bars, I run them until they start to lose grip in the wet at normal speeds on my drive - this is always a bit more tread than the wear bars for me. So I don't buy used tires anywhere except in an emergency, and those get replaced asap. Others may be more expert in evaluating a used tire, or willing to take more risk.

Interesting. I didn't know that. I learned something new!

Thanks!

I purchased the spare tires from bavauto for $249 and went to harbor freight to purchase the jack for $10.00.

hated the stock michelin Run flats, switch them with Conti DWS. Loving it, softer ride, but lost the handling a little bit, conti DWS has soft side-walls.