I will admit that I have no direct experience with a 2 speed pump. I am only repeating what I have read here on many occasions. I guess I'll have to go do some research!
I can say that my variable speed pump is ridiculously cheap to run. I run it at 1100rpm for skimming, filtering and making chlorine and it uses 150 watts at 1100 rpm. At 10.25c/kWh I can run my pump 24x7 at 1100 rpm for less than 12 bucks a month.
Here's a variable speed pump for 650 bucks,
Pentair SuperFlo VS Pump 342001 | Pentair 342001
Update:
I am back with more data to back up the assertion that a two speed pump moves half the water while using 25% (or less) of the electricity.
The Pump Affinity Law
The advantage of a small pump is explained by the Pump Affinity Law, which states that the power consumed by a pump is proportional to the cube of the flow rate. This means, for example, that if a pump’s flow rate is reduced by half, its power draw is reduced to one eighth. If you reduce a pump’s speed from 3,450 rpm to 2,400 rpm — a 30% reduction in speed — the watt draw drops from 2,000 watts to only 593 watts — a 70% reduction in power.
If you reduce the speed of a pump motor by half, you get half the water flow, so you will have to operate the pump for twice as long as you would if you used a pump with a more powerful motor. But since the low-speed motor only draws one-eighth as much power as the high-speed motor, it will only require one-quarter as much energy (in theory; actual savings are somewhat less than theoretical savings) to move the water with a smaller pump.
Read more:
Is Your Pool an Energy Hog? | GreenBuildingAdvisor.com
Variable Speed Pool Pump or Dual Speed... Which is Best for Me? - INYOPools.com
The energy savings that are gained by replacing a single speed pump with either a dual speed or variable speed pump are based on an engineering principle known as the Pump Affinity Law. Without taking you back to high school algebra class, this principle states that the energy savings are disproportionately larger as you lower the speed of your pump. For example if you reduce the RPMs of your pump by 50% you don’t get a 50% energy savings you actually get a 75% energy savings