The seller shouldn't expect to get much out of it, in fact he should consider himself lucky to find a buyer.
On the other hand, it is certainly cheaper to pay $50 for an empty cabinet like that one to build a MAME out of, versus scratch building a cabinet. Way faster and easier, and you can make it identical to a DK/DKJR/etc. if you really wanted. You could purchase repro CP, sideart, bezel and marquee and have a machine that looks nearly new when finished.
It's unfortunate that it doesn't have the brackets, CP, glass, etc. but it would still be easier than building a scratch cabinet.
Wade