I came across one dude who is into gaming, car race simulator, e.g. Forza Horizon and Beam NG drive. 

What he did was: used real car speedometer in the front of the computer monitor and that speedometer was showing the speed and RPM according to the game. Technical implementation of that is open source, a no brainer and overall cost of the relevant parts (e.g. CAN bridge) excluding cost of the actual speedometer is few bucks. Speedometers are generally not that expensive and some cool looking can be purchased from $250 NZD more or less from wrecks. 

I am not into gaming nowadays, but I am an expert in speedometers. I can power them on the bench, I can run them at a speed via CAN bus or turn RPM needle etc. or turn on or off LEDs. I have CAN bus tracer/transmitter and can intercept relevant signals from the actual car.

What is most importantly I have pile of cool looking, non-expensive speedometers from Lexus, Mazda, Toyota, Honda, Nissan, which I no longer need for my developments, which you could utilize for your racing games. Could be fun DIY project for some. 

My major consultant who is always right, said - not worth your time, there will be no takers, nevertheless, crowd opinion matters:  

What do you folks think?