Depends on the price, depends on the gun.
If a gun was robbed of 33% or more (G17/19/20/22, Beretta 92, Full-size 9mm USP's, Rugers, CZ's, *&*'s, etc.) of its designed capacity, I consider it pretty crippled. If it's one to three rounds (G21/23, Beretta 96, most other full-size .40's), then I'm not as determined to track down a full capacity mag.
How stupid do the manufacturers of Beretta 96 or *&* 4006 mags feel when making sure that you can't squeeze that eleventh round in?
I'll shell out bucks willingly under $50. I start to get balky in the $51-$75 price range. Above that dollar figure? Well, I have one Glock 20 mag...