Realistically
I have only very limited funds. I can't get the books now that I would like to. Settings are neat and all but I get so little use out of the various setting material I already buy, that most of these, though fun and interesting, wouldn't make it to my shelf before a winning lottery ticket came my way.
-Planescape
I would sell my children to night hags for their soup if it was the only way I could afford Planescape material.
As it is now, I buy FR to mine for my own fairly high-magic homebrew, and I own a couple other settings, OA, RL and Ghostwalk, and I'm sure that after next year's tax returns, if there's enough money, I'll pick up Eberron, or maybe just races of Eberron, I don't know. Planescape is the only one for which cost is no issue. I will buy Beyond Countless Doorways from Malhavoc as soon as I can, but I really want this team to have the rights to continue Planescape, the one true setting of granduer.