How long do you plan on being a pilot? The PNT will last forever, and when it does wear out later in the century, you send it back and they refurb it for a modest fee. You can replace the wheels yourself (roller-skate wheels), unlike most other suitcases.

Anything cheaper will cost more in hassle factor...you will have to take it to the shop once or twice a year, they won't be able to fix it before your next trip, so you'll need a backup unit too.

If you're really strapped I'd get a cheap flight case and spend the dough on the PNT.