The best way to estimate your savings with Edges is to check your usage numbers, not just your dollar figure. Find out what the charge per therm is. Take the Edge numbers (therms/hour) and calculate.
Prices are different everywhere. You really are the only one that can answer your questions.
For me, with pricing here, the difference between a rebuilt MM360 and an Edge 60 was about 12%. Payoff came to something like 58 months. It’s not worth it to me, at this point, to spend double the amount for those “savings”. I"m not saying the Edge folks are saying anything wrong, just that comparisons I’ve made here don’t justify the expense.