My HVAC guy charged me $500 for the part and labor to replace the relay switch on my gas furnace. This seems excessive given the prices I see this type of part, and the labor which took less than 30 min. Is this company of the level?

You pay for more than the just 30 minutes he was at your house... there is also the time to drive to and from it... Techs can spend half of their day just driving to and from one customer or another, the deserve to get paid for more than half the day they are at someone's house... that's why there are minimum charges.