Diagnostic readings on 01 taco

I was wondering what an average cost if a diagnostic reading is. I had my check engine light come on the other day after making it through a yellow light. Shut it down checked the gas cap and turned it over and the clock that never worked came on. So my garage is closed today and now im sitting at a firestone. Diagnostic charge was 105 bucks. I drove a 79 ford 150 for the past 15yrs so its a bit of a shock on the price. The check engine light was off when I started the truck today and the light was off. Thought it would be best to have it checked even though its runnin fine

 

Glad I went in, had it taken care of ened up being the throtle position sensor. Pricy part at $120 bucks.