Can I replace a high limit switch myself?
You might be able to do it yourself.

Google for "service instructions &lt;brand and model>" of the furnace to determine where the limit switch is located.  With power disconnected, open the necessary panel(s) to assess whether it is something you would be comfortable doing.  It may require removal of the blower assembly and/or reaching past sharp and delicate heat exchanger protuberances.  Or it could be right there, front and center held in by only one simple screw.  It is well worth taking a look.

If you decide you aren't up for replacing it, you don't have to call an HVAC company.  Maybe you have a handy friend, relative, or neighbor?  In such a case, etiquette calls for exchanging their services and skills with a tasty drink or meal, depending upon how much you value their help.