Taking it to a mechanic costs you quickly $90, just to read the computer error code and do an analysis. Last time the diagnosis was: "nothing to worry about, carry on". Cha-ching $90. The time before that the diagnosis was: "your catalyst converter has a misreading. Let me clear the light, if it comes back on, we'll need to probe again. Carry on." Cha-ching $90.
Since many years now, all car computers have a standard connector and a standard protocol to communicate with the car computer. It is called ODB-II.One thing my car lacks is a simple: reset-check-engine-light button. This would allow me to reset the light to verify if it were a temporary event, or whether the failure persists. Honda are you reading this? (likely not)
Your next bet is to purchase an OBB-II reader. These OBD-II readers are available at Kragen and Wallmart and cost you from $60 to a couple of hundred dollars. After reading out the code (indeed, again the catalytic converter), the light hasn't come on again. Saved $90.
Many gas stations provide water and air. How about adding an ODB-II reader?