You can buy those metal sensor sheaths separately. Search for something like "rtd sheath metal" e.g. ebay #162885663706. $2-3 for a set of 5. Then you pot the

You can buy those metal sensor sheaths separately. Search for something like "rtd sheath metal" e.g. ebay #162885663706. $2-3 for a set of 5. Then you pot the sensor with something thermally conductive and waterproof - waterproof potting compound is cheap (e.g. "RS PRO White Epoxy Potting Compound"). Finally heatshrink the outside. You will never beat China prices, but this is one of those parts that's relatively easy to make yourself and shouldn't cost a fortune. The most expensive stuff is the epoxy, but it will last for a while. Purely on performance, does it matter? If it doesn't matter if you're off by a degree or two, then the cheap versions will be OK. If you need the guarantee of a genuine sensor, or a different cable length, or whatever, it'll cost about $20 for five.