At Pool Pros we only recomend the Hayward Universal Induced Draft Heater. This heater in the H250FDN Size range will heat any above ground pool with ease. A Heater of this size will cost around $2,000.00.
This heater will require a concrete pad to be set on. This will cost $150.00 for a concrete pad to be made for the heater and filter system.
Then you need to plumb the heat to the filter system. This will be abother $150.00
Then you will need a licensed HVAC Specialist to run a supply line to the heater. This gas line run can vary from $600.00 to over $1,200.00 and is completley dependant on the length of run. The shorter the run the lower the cost.
This heater has an electrcin control so it will need and electircal supply as well. IF there is an outlet at the equipment pad it can be wired to be plugged right into that outlet.
In the end your are talking in the $3,500.00 and up ball park for a heater, concrete pad and all utilities installed to it so it can operate.