Depends on what you want it for. If it is for a compensator then a cheap on will do since these are short and alingment isn't as critical.
If you intend to attatch a suppressor then don't skimp on a cheap barrel. The reason I say this is that cheap barrels often have misaligned threads. If the suppressor is off by even just a few degrees the bullet will strike the baffels and then your can is f**ked!
A good barrel from Irv at
Bar-Sto will cost you a bit (mine was $232 including cutting to length, threading, and shipping for my Glock 21) That's not much more than the Transfer Tax that you'll pay for a new suppressor when you mess up the other one.
Just my $0.02
Also check out
Gemtech for a list of other recommended people for extended/threaded barrels