Not all tint is created equal. Not saying this is the reason for the price you got quoted, but sometimes the more expensive places are using the better 3M films or Llumar/Formula One films. Those are MUCH better than the cheap tinting places and you will pay more for them.
The better films are optically clearer, have less glare, filter UV almost completely, don't interfere with the radio and reject a significant amount of the heat. Quality costs money.
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