I currently have the luxury of storage space. However during college and a year in Ameri*Corps, all my minis stayed in a closet/attic at folks' house.
There are many options that are more cost effective than a GW miniatures case. I have a 3 old gray chessex cases, 2 Doskocil 2 layer pistol cases, 1 gw case I bought used, 1 single layer pistol case, 1 shotgun take-down case, and a few of these: Plano 4 pistol cases
I don't own any guns. GW used to sell rebranded pistol cases from other manufacturers before they created their 'own' miniature cases. I'd recommend the Plano 4's, they have a lot of space, good foam (and by that I mean fairly dense, with a deep egg crating which holds models in place really well), and are pretty inexpensive.
I'd avoid the shotgun cases, at least mine doesn't close tightly enough to keep my models in place when I pick it up and move it. Its fine for storage, but not so much for travel.
I hope that helps!
edit - I've sold a few armies over the years, usually just from being tired and wanting to start a new army. And in most cases I've found that the sale didn't generate the cash I wanted. At this point I find I'm too invested in the time and effort expended on converting miniatures (not so much the money) to sell them off. Besides, after years of playing chaos in various forms, I like haveing a smorgasbord of things to choose from when writing an army.