Plastic or pewter?
Pewter I have in a nice, hard-side-plastic, molded, foam-line case with slots cut into the foam to protect my hard work and beautiful paint jobs. It's from Games Workshop and runs around... maybe 30 bucks? Been a while since I got it.
Plastic, like the new WotC line? I'm with Henry, almost. I picked up some cheap, $1.99, plastic, non-lined, translucent, plastic cases from my local Hobby Lobby arts and crafts store. I picked up three over by the beads aisle and have over a hundred minis crammed into them, despite their only having 16 smaller sots and 1 larger slot. They are much wider and deeper than the foam slots in my GW case and can hold quite a few minis in each slot. Heck, I can fit two large creaures (dire boars) in one large slot and still have room to pile a few other minis in there if I wanted too. I even have some large wooden buttons that are meant to serve as tables in case my players get into a barroom brawl.
All in all, it depends on how much you care about your minis. I've been to many a Warhammer night at the LGS and seen everything from expensive metal cases that you could throw off of a cliff and still recover your minis in fair condition to shoeboxes loaded with some of the most beautifully painted undead I have ever seen.
