re: selling/buying a kidney – The problem of dina d’malchusa dina, comes to mind. (But I would tend to view it similarly to you, that pikuach nefesh is a powerful thing). A shailah should be asked.
And though a person can “live” with dialysis, unless people have been through the process (I B”H have not), they are not really qualified to determine if that is any kind of a life for the person who is forced to endure it several times a week. This is a very difficult issue. Al pi halacha a live donor may donate a kidney. However, kidney donation is not as glatt and easy a thing to do as some people who are great proponents of it would have us believe. IT IS MAJOR SURGERY, and as with any major surgery (or even minor, for that matter), there are risks of injury or death. Forget about the idea of “special shmirah” because you are trying to save a life. Plenty of people lost their lives trying to save other Jews. There are risks with anaesthesia, risk of infection, risk of embolism, risk of post-surgical complications, and the person who loses one kidney, is now at risk should anything happen to the remaining kidney.
If chalilah v’chas it was a loved one and I were a match and suitable as a donor in other respects, IN A HEARTBEAT I would do it. But many people are being asked to do this for a complete stranger, and the issue is not as simple as it is made out to be. Each person needs to look into his own conscience, speak with a rov, and make a decision if ever needed, lo aleinu. May all Klal Yisroel have good health and arichas yamim.