Monster Bash used to cost alot more, I have seen decent ones sell between 7 and 8 grand fully redecalled and fully stripped down and rebuilt.. They are now top dollar at 8 grand.
Remember, u are now talking about a apx 16 year old title now. I would buy a AC/DC Premium over the Monsterbash after playing both.
The new Sterns are now making some of the older titles look old now. Monsterbash is a really nice looking pin with good audio.
There are plenty of MB floating around for resale etc, but once the Premium Ac/DC sells out, it will be hard to find one.
Play both then decide.