cost...I have no idea.
If you can weld and you have a chop saw and some correctly sized DOM then you could do it. there's a writeup in the YJ tech section on Jeepforum I believe--I think Joe Dillard did this when his dana 30 cracked at the CAD.
I was thinking about doing this, but D44s are common enough that they can be found with the welded wedges, or a leaf sprung model.
I believe you could use the gears etc, but I am not 100% sure. someone else may know better than I do.
the shafts could be different lengths. then you would want flat top knuckles--chevy is preffered I think, so then you would have to run chevy outer shafts, chevy brakes etc with the chevy knuckles.
Mr. N's site has a TON of information on all of these different d44 models. I read through it a few times, and then ultimately decided on a d60 front instead.
