In order to obtain accurate tire pressures, you need an accurate tire pressure gauge. However, without a known good source (KGS) to use as a reference, the accuracy of the gauge is unknown. Certainly, a tire pressure gauge that is more expensive is also more likely to be more accurate. To check the accuracy of your gauge, take and record multiple readings from the same tire. As long as the readings are within +/- 2 psi of each other, the gauge is as accurate as you can expect, without spending a fortune. Indeed, measuring techniques cause more inaccuracies than the type of gauge used.
For more info, see How to Use a Tire Pressure Gauge