Where can I buy an ignitor for this heater which

Where can I buy an ignitor for this heater which is about 7 years old. I like the heater very much but the cheapest price I can find an ignitor for is around $ 50 to $70 and I can buy a new heater ( another brand ) for a little over $ 100 at Lowes. I would like to fix the heater I have as it really works well when it runs. It ran for 7 years without anything done to it and that sells the product to me. Thank you, Lee Green