Pool heater replacement

My pool heater needs replacement.  It was installed with the new pool in 2006.  We rarely used the heater, and apparently rodents may have damaged the wiring.  As I contemplate replacement, I have several thoughts:

#1 Would it be cheaper to buy the heating unit online and find someone to install the unit?

#2 Should I consider replacing the natural gas unit with a heat pump that will not require the natural gas.