Can't offer a good price estimate, but I can attest to the build quality of that top box. I have one that looks identical that I bought as a 19-old new hire at Great Dane. I think I paid $500 back then (around 1998) for it along with a bottom chest (similar to yours, albeit with the top three drawers replaced by seven smaller drawers configured like the top box) and intermediate chest.
Mine is ugly as hell, spray painted forest green with some half-*** welded repairs, but it spent its first life in another mechanic's hands before moving to three shops and ultimately getting banged around in the back of a service truck for 18 months. It's sitting in storage now, waiting for my eventual retirement when it will find its last home (with me) in Louisiana.