I have heard of this being done, on several occasions.
Cost is not worth it unless it has sentimental value or you are 'one of those guys, who do silly things (I am in that category, so...

)
1. Cost of frame to cut up, if lucky someone has a messed up frame but that is harder to obtain ($50 if very luck, but most likely $200-$250)
2. Cutting and then welding the old to the new x2 (kinda) so what $200
3. Fixing and then rebluing properly (kinda in the above, but many times, the fixing and rebluing are separate) $100-$300 (or more)
So, by the time you get done, I would guess a $300 if lucky, but I think $600-$800 for a project like that?
just my 2 cents
Ed