Break-even index / RTX 3090 (used) / GPT-5.5 / Tennessee
Will a Used RTX 3090 rig beat GPT-5.5 in Tennessee?
Your rig pays for itself in 5 months — after that you bank roughly $223/mo versus the cloud. Clear win.
How to read it: OWN — the rig pays for itself inside 18 months. HYBRID — break-even lands between 18 and 36 months; real, but slow. RENT — it never pays off before the hardware is due for replacement. Every formula and threshold is public on the methodology page.
The numbers
| Build cost (Used RTX 3090 rig) | $1,200 ($1,100–$1,300) |
|---|---|
| Hardware amortized (3 yr) | $33.33/mo |
| Electricity in Tennessee ($0.130/kWh) | $6.24/mo (48 kWh) |
| Local total cost of ownership | $39.57/mo |
| GPT-5.5 at the same usage | $263/mo |
| Break-even | about 5 months |
Assumes the "coding assistant" preset: ~15M tokens/month, 3 h/day active, 5 h/day idle. GPT-5.5 priced at $5/M in, $30/M out (verified 2026-07-05). Rig ceiling: Up to ~32B models at Q4 — 70B is tight. Jargon: VRAM is the GPU memory that decides which models fit; Q4 is 4-bit quantization — a smaller, faster copy of a model with a slight quality cost.
See your verdict — then tweak every number →