They still have G19's for well under $600 here locally. I just bought a like new Gen4 G23 for $469 at my LGS the other day, which is pretty much the same gun and can become a G19 with the addition of a $100 barrel.
If someone has their sights set squarely on a specific high capacity pistol but is without the current funds...it might be worth buying a couple mags for your future purchase. You will almost certianly be able to get the gun later, it just might come stock with 10rd magazines. Then you'll have a couple pre-ban hi-cap mags to go with it. I've actually been considering this for the M1A I wish to someday possess.
AR mags are a little tough to come by right now. But I believe most pistol magazines can be found at reasonable prices if you know where to look. Yes, even Glock mags. G18 mags are going for insane prices ($80-300) on auction sites, yet there are places that have them in stock right now for under $50.