I paid 36,000 for my brand new 2012 3500 ST , which is a "base" model truck but it had all the mechanicals I wanted . My buddy bought a nearly identical truck except a 2013 model with the aisin transmission 1 year later for 38,000 . Both of our trucks have cruise ,tilt, power windows and locks , keyless entry ( mine has auto start) satelite radio, ect . It's a very nice truck and does not feel base model at all ( the 2013 has a backup camera )
I looked for a solid year trying to find a good used cummins but the prices where just so high I decided on a new one . I looked at GM and ford offerings but the prices on those trucks were much higher for less especially with an inferior engine.
As for the new engine in the old truck , you have to do it out of love for the old truck money wise it's a wash . To do it right the conversion is going to cost a minimum 10,000 plus the clean square body crew cab and then your still left with a rougher riding , noisy , drafty truck , that won't handle as much weight as the truck the engine came from. In my option to do it right you need to blow the truck completely apart box ,the frame , lizard skin and dynamat the hell out of the cab and doors , find a ford 60 front end ( or convert over to coil sprung front using a AAM axles from the donor rig ) swap out the rear end, beef up the rear suspension , and then figure out how to make the cruise control, gauges, A/C all work like they should with the factory appearing GM gauge cluster . It's alit off work to do it right it can be done but it takes lots of time and money.
I just want to make sure if I go with an square body that it doesn't turn into another project. Sure, I can change some stuff down the road if I feel like it, but I don't want something half-finished. 
Nevermind.
Obviously it's a few months out until I need to pull the trigger on something, but I don't want to not have something at least mostly lined up by the time we move and are also going to be looking at houses, and everything else logistically.
