The watercooling flow meters would be a total shot in the dark. Since most of them are made in the EU, they
used to be cheap.
Innovatek Flow Meter Rev. 2.0 - $45 (€30)
Most legitimate fuel flow meters I've found are intended for constant flow applications (aviation, marine). They require pulse dampeners, lose accuracy with fluctuating flow rates, and are expensive. The smallest one I've found is rated at 0.3-30gph.
Floscan 201A-6 - $110 ($148 w/ pulsation dampener)
Another cheap solution might be employing a MAP and IAT sensor to calculate MAF. If you can calculate the AFR to any reasonable accuracy, the fuel rate can be determined.
- LostCause