1 A portable air compressor with a 6.5 HP gas engine, 10 gallon tank, and 135 PSI might cost roughly $750 to $1,250. 2  For around $2,000, you can purchase:  An Ingersoll Rand portable air compressor with a 7.5 horsepower, two-stage electric motor, 80 gallon vertical tank, and maximum pressure of 175 PSI.