You've probably seen the ads in the back of the Pro Audio mags, or been in one at trade shows.
Professional sound isolation for musicians, recording studio 6x8x7 feet, Door with glass, twin ventilation fans, cable passage s. Modular construction, can be moved. Sits on floor. Built in sections, strapped together. MDF with gray carpet covering. Used in a/c studio, no smoke.
New cost over 7k. One sold used on ebay for 3900, I'll do MUCH better than that. Make an offer.
My buddy in Boston area has stored it in his studio since 2003. Local pickup, requires 2 strong people and truck to move.