The original poster said that he/she wasn’t concerned about compensation for time so I think you’d be looking at $5 – 6K for the kit, trailer, electrical, supplies, etc. I would recommend doing some Craig’s list searching in your area to see what used trailers are going for. As CLC has pointed out in the past, at some point you start competing with used RVs that, while not as unique, can offer more amenities/space.
One thing to double check are the state laws regarding selling the trailer/RV. It seems like some states let you just register the trailer as a utility trailer while others require it to be registered as an RV. Also, if you make any modifications to the trailer, like with the Northern Tools kit, you might get some questions when selling it. Worth double checking to know what you are getting into. If you’re not taking it on the road, you could let the buyer be the first to register/title it.
That being said, my gut tells me you could find someone to buy it for 5 or 6K.
-mike