It's doable - there are folks that offer it as an industrial solution.
It's quite hard to do it DIY. GPS doesn't work indoors. Pixyz says it does, but it was expensive the last time I looked. Some people use large GFID antennas on chokepoints and a GFIS tag on the forklift - you mat be able do inventory management at the same time.
Basically though, it tends to be expensive, because it's tricky to do. A home-brew situation is going to be time consuming and hard to get right.