All of the responses are good in this thread.
As a chemist who used to produce thermistors a long time ago, I can say that $250 is definitely out of line. As a matter of fact, I consider Linn wanting $15 for the replacement to also be unreasonable. The materials involved(combined oxides of various metals such as cobalt, copper, iron, manganese, nickel, etc. pressed into a disk using a lubricant to hold it together, and calcined) are extremely low in cost. Usually, the most important thing is the attachment of leads(which could be your problem); trying to achieve an ohmic contact. However, I do understand the desire to use an OEM replacement...
Thermistors may be NTC(resistance drops as temperature increases, like a typical metal oxide), or PTC(resistance rises as temperature increases, like a typical metal). The two characteristic values of note for a thermistor are TCR(Temperature Coefficient of Resistance - positive for PTC, negative for NTC) and Beta(which is derived from TCR). These would be two things you should try to match(they are a function of the thermistor material), in addition to physical size, etc.
As a chemist who used to produce thermistors a long time ago, I can say that $250 is definitely out of line. As a matter of fact, I consider Linn wanting $15 for the replacement to also be unreasonable. The materials involved(combined oxides of various metals such as cobalt, copper, iron, manganese, nickel, etc. pressed into a disk using a lubricant to hold it together, and calcined) are extremely low in cost. Usually, the most important thing is the attachment of leads(which could be your problem); trying to achieve an ohmic contact. However, I do understand the desire to use an OEM replacement...
Thermistors may be NTC(resistance drops as temperature increases, like a typical metal oxide), or PTC(resistance rises as temperature increases, like a typical metal). The two characteristic values of note for a thermistor are TCR(Temperature Coefficient of Resistance - positive for PTC, negative for NTC) and Beta(which is derived from TCR). These would be two things you should try to match(they are a function of the thermistor material), in addition to physical size, etc.