We had a different experience than most of the replies.
We bought a 25B Classic. We searched high and low for the B floorplan, because as luck would have it, we decided to size up from our Bambi just as that floorplan was being discontinued. We found one, a Classic and the price was right but it was a queen and we wanted twins. We bought it anyway and Pete removed the queen and built the twins.
Cost of materials a couple of hundred dollars plus the cost of the new mattresses that were custom sized foam plus getting them covered in a nice bark cloth. $600 tops total.
Hours of work--All approx.--tear out--4-5 hours, building the new platforms--4-5 hours, installing--3-4 hours.
If you want to PM me, we have pictures (somewhere) of the whole project. We did this 3 years ago. And if you want, we can chat over the phone for the details.
It was an easy, fun project, we had never done any kind of trailer remodeling before. And now we have the additional space in the bedroom and no bickering over how warm to keep the electric blanket!!!