Considering that you can get a new Hayward heater installed for $2,000 - $2,500, the gas company's prices is excessive.

Do you mean burner tray, or heat exchanger? $900 is not necessarily out of line for the heat exchanger, but it is for a burner tray. I think you need to see if you can have a knowledgeable local pool guy take a look. Spending $100 to have some give you more reliable hands-on info would be worthwhile, under the circumstances, I think.

The consensus that the Hayward is better, is from here, and it's an informal rather than formal thing. One key point is that only the Hayward offers salt compatibility on their standard heater. Another is that Pentair has drastically cut its warranty on direct-to-consumer sales.