looking at purchasing a second hand Dynojet.

facts

• cheap
• no computer or software
• no retardation device
• no o2 setup
• possibly no module and cables
• 12 hours drive away
• can add o2 and eddy current retarder easily (but not cheaply) at a later date
• software for Dynojet seems to be available for a nominal fee once you give the company the serial numbers

considering the effort and expense required to build an inertia dyno and put in suitable sensors this may be a good option.