The cheapest would be to remove all the front end suspension related parts, put in a custom solid axle swap, brakes & steering, a divorced transfercase. new crossmember or 2, 2 new driveshafts, the transfercase linkages, about a 6" lift put back so you won't drive around ass low all the time.
I would *GUESS* 5 to 8k.
keep in mind, this would make your truck more capable offroad then all the 4x4 factory, and lifted trucks. Add a pair of lockers (if you don't already have one) and you would be at the top of the heap for capability..