Every pool is going to be different and it depends on how much effort the pool owner has put in to making the pool energy efficient. But some of the biggest factors are going to be the following:

Pool Size - Larger pools require more pump time and more chemicals. The cost is pretty linear with volume so just figure a pool the twice size is going to cost twice as much to operate, assuming everything else is the same.

Pump Size - Large HP pumps use more energy per gallon of water pumped. Two speeds and variable speeds are much more efficient and can cut energy costs in half. If the houses you are looking at have pools with large single speed pumps, figure that you will need to replace at least the motor to get some efficiency.

Heating - Heating any pool can be expensive if you are using gas or electricity. However passive solar panels can be a very inexpensive way to reduce costs.

Solar Cover - Prevents heat loss through evaporation so it saves both water and heat costs. A pool with an autocover can be a real cost saver.

Pool Maintenance - DIY, it really isn't that hard plus most pool services really don't know what they are doing.

But in general, you can make almost any pool more energy efficient. It takes a little knowledge and sometimes extra money.

I am in No CA and have put some effort into minimizing costs so here are some of my stats:

Pool Size: 20k gallons
Pump Size: 1/2 HP 2 Speed Pump
Heat: EPDM Solar Panels
Chlorinator: SWG
Solar Cover: Most of the summer
Summer run time: 1 Turnover per day (120 kwh/month)
Winter run time: 1/2 Turnover per day (60 kwh/month)

don't forget water bill. i suggest putting a ball valve on your overflow to capture as much rainwater as possible to lower water bill.

Regarding the water bill, is there some rule of thumb for percentage of water expected to be lost/replaced every month? I assume things like waterfalls, fountains, etc. would increase it significantly?

I would not put water costs in the most significant category and I posted before, you can manage water loss with a solar cover. Without a cover, the evaporation loss will depend on the surface area of the pool, the water temperature and the dew point temperature.

Below is a link for evaporation rates for unheated pan tests. This would be the minimum loss without a cover and without additional heat. For me, it is 60" per year which equates to 2750 cu-ft and our water rate is around $2/100 cu-ft so about $54/year. Halve that if you are using a cover half the time and double it if you don't use a cover AND have solar. But for most pools, the pump and heating energy cost will well exceed the water cost.

Here is a link that might be useful: {{!gwi}}

Great info, thank you.