The biggest issue, apart from Phleas, is that the possible savings are pretty much unknown. If you can save $400 over the summer, than it still makes sense. If not, then the payback period will be stretched out over a couple of years (assuming it works).
It seems the cheapest option to get rid of the scale is the filter I posted earlier at ~$55.
The second cheapest option I could find was a 35psi, 1gpm pump at ~$50. Unfortunately, it's only 12VDC. The 115VAC version cost ~$100. If you have a spare battery and charger or power brick than it might work out.
Aquatec 2800 (40psi, 1.0gpm, 12VDC) ~$50
Flojet Fl-12V (35psi, 1.1gpm, 12VDC) ~$50
Flojet FL-33 (35psi, 3.3gpm, 115VAC) ~$100
- LostCause