Leasing the tank seems to be the way to go, if you're ok with an above ground install. Much cheaper to do a yearly lease fee than buy one outright, plus they service it. (and of course, it's already there if the SHTF, so not like they will come and get back). This would dramatically reduce the cost outlay (especially as it will take a lot of $ to actually fill the tank too). I'm really liking this paired with a propane generator though. And in short term issues (like power outages, etc.), having the full power capability (and with seamless transition) throughout the house is simply too cool for words.
Granted, post SHTF, we'd enact some strict power usage rules, to stretch the supply out.