I don't know exactly what the state of the art is now in MEMS gyros, but I'm pretty sure the tomahawk uses mechanical or ring laser gyros. Those systems are expensive.

For the reliability/storability parts though, the electronics are probably the least of the issues. You've got a jet engine in there that needs fuel, oil, and has a number of high speed moving parts. Having something like that sit for years in a ship and work with high reliability is not so simple.