As to it's worth, It is only a 3 drawer box - for me a BIG negative. It IS a Proto so it will be a cut above the pack, as Proto was not contracting with the mid/low end box makers for their branded boxes, and as a collector piece, probably worth the asking price.
I really have dismissed the rollers without full drawer for effective tools storage, mostly because its a waste of floor space when you have as many boxes as I do.
IF it was in perfect condition, I might relent, since I don't as yet have any Proto Boxes, and would like one for my Proto/plvmb tools, so I'd probably die of indecision on the spot.
Generally I try to target rollers like that at around $10 a drawer for the usual suspects. Some, as with anything, will command a premium, and some (The bottom feeders) are not even worth opening a drawer, other than to see what might be inside...