I'll play
If I'm already set (as I feel I am), and I have $500 that I
must spend on ammo...
I'm going boutique, non-standard caliber for lower-priced surplus pistols.
I've found 2 places that load for 9x23 Largo (new Starline brass, good quality components), and their prices haven't skyrocketed compared to the rest of the market. One sells 50 rds FMJ for $30, the other sells 50 rds JHP for $36. I've shot some of the FMJ already and it ran great. We have a pair of Star Modelo Supers, each has a 9x19 and a 9x23 barrel. Mags etc work with both, just swap barrels and you're good.
Right now, it's cheaper to shoot new Largo than new 9mm Parabellum, so we've been playing with them.
Another I'm highly interested in, 7.65 French Long (Longue). I remember seeing the French pistols a number of years back, at the time ammo was non-existent. Which was a shame, because the guns seemed to be very well made, basically precursor to the Sig P210. One of those ammo makers now rolls that stuff for $27 a box of 50, and I'd really love to pick one of those guns up if I could.