[Relaxing]

Here's the easiest way.

// global vars
float gKill[33] = 1.0
float gDiscount[33]
new gPrintDiscount[33]

gKill[id] -= 0.01 // on client_kill
gPrintDiscount[id]++ // on client_kill

new full_price = 16000 // price of item
gDiscount[id] = full_price * gKill[id] // new price

if (gKill[id] <= 0) gDiscount[id] = 0; // free item, after 100 kills;
if (gPrintDiscount[id] > 100) gPrintDiscount[id] = 100;