It depends on how much time you want to spend looking for it

I have about 2200 45 brass at the moment. Next time I go to the range, I'll shoot 200 rounds, and pick up on average about 180 brass. If i spent an extra hour scourign the landscape for those 20 pieces, i would never need more than 200 brass. As there are much better things I can think of doing with an hour of my time (like reloading some of the brass that I DID recover), it's a good trade off for me. Similarly, I have about 700 38SPL brass, and never lose ANY. Though after 15 or 20 firings they can crack, get loose primer pockets, etc, and I'll toss a few.
There's no real cut and dry answer, but IMO there is no such thing as too much. There IS such a thing as not enough.
You guys got me to thinking, and I worked this out:
Powder: Alliant Red Dot $25/lb (skeet club buys bulk)
Primers: CCI Lg Pistol $50/1000 (primers are expensive here)
Bullets: Cast 230gr tumble lube $30/4500 (20 bucks for a bucket of wheel weights equals out to about 150lbs of ingots and 10 bucks for lube)
Brass: Norc Brass $70/1000 (average 10 firings)
Powder Charge 4.2gr
Price per 1000: $77 even. Plus countless hours of melting/fluxing/casting/lubing/polishing/trimming/charging/seating/crimping ETC