These are worth at least $100, and there's a set on eBay for $75 + shipping.
The Monsoon MH-502 is long discontinued, and a "like new" in-box set is a very rare find.
Finding an undamaged, complete set -- period -- is a difficult task!
Get it here:
http://cgi.ebay.com/130530929062
If I needed more sets (but we don't, we have plenty!), I'd be all over that deal.
Hopefully somebody here will snap those up.
Expanded details on the Monsoon line is one of the articles being developed for summer release on this site.
Sort of jumping the gun here by discussing the topic. But wanted to pass along the find, while it exists!