The ideal buying price point in my opinion is about $120 - $150. I've been kind of breaking that rule lately though. Spent $199 last November for a "top of the line" Leadtek GF3 TI-200. It's now worth maybe $70. Gave it to my wife. Spent $229 yesterday for an Asus GF3 TI4600.
Hmm lets see here now.
Voodoo Rush - Paid $200ish new, worth $5 at best today
Voodoo Banshee - Paid $100? new maybe, worth $5 today
TNT1 - Paid $150 new, worth $8 today
TNT2 - Paid $130 new, worth $9 today
Voodoo 3 3000 32mb - Paid $120 used, worth $20 today
Geforce1 sdr 32mb - Paid $150 used, worth $25 today
Geforce2 32mb ddr - Paid $135 new, worth $45 today
Radeon 7000 32mb ddr - Paid $40 new, worth $30 today
Geforce3 Ti200 - 64mb ddr - Paid $199 new, worth $70 today
Based on this it will be about 2 years from release...