I put wheels on a couple of mine that I've had for awhile...
Besides bragging about what a great deal I found...

Any decent tool box will set you back a lot of money, and most don't come anywhere close to the quality of these card files.
Map drawers/flat files also make great tool and parts storage.

In the parking lot ready to load
Here they are on the trailer
And in the new shop in the parts room
This picture is of some of the ones I have at home; 28" deep, full extension slides!
Rob