For the hardcore builder: This uses a brass fitting from the hardware store, a small spring, GG-J type thermocouple wire. You can view the wires at Omega.com but there is lots of cheap wire on ebay. Search ebay for glass thermocouple wire. Any type J will do but the glass-covered wire is stouter and will not care about hot exhausts nearby.
The spring will push the balled-up sensor up against the cylinder. Twist the two wire ends together and roll them into a ball with needle-nose pliers. Silver-solder the ball (lots of tutorials on Youtube). Wash off flux. Cut wire to length and fit spring and brass fitting
Sparkplug types can also be made. Start with a copper washer, clean it bright, apply Wite-Out where you don't want the silver solder to flow (called "resist" in the jewelry world"). Twist the T-couple wire a couple of turns and silver-solder to the washer. For a better-supported device, bend a piece of stainless welding wire and solder it too, wash off the flux. Below are a couple I made for a bike. The trick is to avoid excess silver-solder which will interfere with the seal.
There are lots of uses for silver-solder skill. Making primer lines is another one.
Time or money, take your choice. :-)