A barrel and the extractor are all that is needed. It would be fun, but I think .445 Supermag would be even more fun, you could run .44 Mags, .44 Specials, and the .445 through it and the cost would be the same.
Depends on how you look at it. For a shooter yes it's a lot. For a rare rifle still new in the box...not so much. The cheapest No.3 I personally ever seen for sale was $400 and that was a few years back and it was a more "common" 223.
I would bet you are going to shell out at least $700 for a shooter grade No.3 in a 44!! The days of cheap No.3's and No.1's are gone IMO.