A DGX Spark bought to resell tokens at $1 per million, at 20% duty, does not pay back. A box you already own only owes the electricity.
Street price comes back only if the tokens, at $1 per million, beat the watts. A Spark bought to resell that rate does not.
Update, 29 Sep: price and demand change the answer
The table below assumed $1 per million for every model and 20% of the day busy. Hosts now set their own price, and uncensored builds start at $4 per million because the big providers do not serve them. Served every second of the month at $4, an M4 Pro at 85.5 tok/s grosses about $899, and after the host's 80% share and the power bill it pays back in about 3 months. A DGX Spark at 79.5 tok/s grosses about $836 and pays back in about 8. The limit is no longer the price. It is enough paying callers to keep a box busy.
The clock
The payback table on /payback uses the US street price, residential power at 18.34¢/kWh, $1 per million tokens, and 20% of the day serving. Months are the street price divided by what is left after the power bill. Watts follow the work.
Fast
The top row is Qwen3.5 2B on an RTX 5090: 351 tok/s, $4,639, 575 W, 2.3 years. That print is /pair/qwen35-2b-q4km-5090. Next is an M4 Pro at $2,199 and 45 W. Qwen3.6-35B-A3B at 85.5 tok/s is 4.2 years, /pair/qwen36-35b-4bit-mlx-m4pro. Qwen3.5-4B at 82.8 tok/s is 4.3 years, /pair/qwen35-4b-4bit-mlx-m4pro. The mini is fast because the watts are almost nothing. The 5090 is not a cheap card. It is fast because 351 tok/s still clears 575 W at $1 per million.
Slow
One DGX Spark is $4,999 on the street table. Qwen3.8-Flash-Next at 79.5 tok/s and 240 W is 12 years, /pair/qwen38-flash-exl3-spark. Two Sparks at 94.4 tok/s and 480 W are 23 years, /pair/qwen36-35b-abliterated-nvfp4-spark. Two Sparks at 45 tok/s are 77 years, /pair/qwen38-flash-fp8-spark. An RTX 4090 at $4,495, 40.7 tok/s, 450 W is 40 years, /pair/qwen38-27b-ud-q4k-xl-4090. The power hour eats a weak token hour.
Cheap, or already yours
The cheap US price on this desk is the RTX 5060 Ti 16GB at $614. Its best quoted decode is 23 tok/s, 180 W, 7.0 years, /pair/qwen38-27b-gsq-rco-5060ti. The 10 tok/s uncensored print on the same card is 117 years, /pair/qwen38-27b-turbofc-uncen-5060ti. A cheap card pays back only when decode is high relative to watts. A box you already own has nothing left to pay back but the electricity. Buying a Spark to resell $1 per million tokens at 20% duty is the long case. The full rank is /payback.