Exhaust Manifold Replacement- new or used?

[Sylvanite]

I discovered today that my exhaust manifold needs to be replaced (#4 header is cracked, just like in the picture that's somewhere on this site). Are there any issues with pulling an OE one off a junk car and putting it on mine? I'd rather pay $25 for one from the junkyard than $200+ for a new one (this is almost as much as I paid for the car).

Or for that matter, could I get my friend to weld the crack to reseal it?