I thought about doing this also after I bought my Hybrid and just looked through a parts catalog comparing liftgate parts between LTZ and Hybrid.
I assumed I would swap like parts like weatherstrip and wiper. But because of the different weights of the door, all the bracketry needs to be swapped also.
Here are my notes on the parts cost if you bought new stuff. I suppose you could take the parts off a wrecked one but you would need a pretty good list to know you picked all the right parts!
Total: $2,940.39
Hinge (Right) $21.66
Hinge (Left) $21.66
Gate $787.80
Support Cylinder (Right) $49.60
Support Cylinder (Left) $48.65
Ball Stud (Right) $6.20
Ball Stud (Left) $4.14
Glass $565.06
Glass Cylinder (Right) $23.61
Glass Cylinder (Left) $23.61
Weather Strip $35.56
Control Switch $13.51
Lower Trim Panel $136.03
Pull Handle $25.18
Pull Strap $32.19
Actuator Rod $43.32
Actuator Rod Bracket $16.67
Control Module $462.98
Harness $141.91
Door Latch $177.09
Window Latch $100.44
Motor $143.88
Mount Bracket $38.56
Release Switch $21.08
After all this, I realized too that you would need a new remote also (~$300) that would have to be programmed by the dealer (~$150) to match the truck and you wouldnt have the cockpit controls..those were another couple hundred.
Also, installation means probably removing the entire interior because you have to change the wire harness... a job like that would probably be best done by a professional custom shop and I would bet you would spend over $5,000 really quick by the time you added parts to labor...
...I decided that I could live with an unpowered lift gate.