Hello Jamie,
What you want to do, is actually, very simple..
I have a remote cabin, with no power, except what I create, and for several years, have been running off a 65 watt solar panel and batteries !!
I recently added a wind generator -- but, back to your water supply !!
Above my cabin, I have a 1350 gallon water tank, that gives me about 2 PSI water flow by gravity alone -- but I have a 12 volt Shurflo pump that supplys 2.8 gallons a minute and shuts off, automatically at 45 PSI -- comes on again, when a valve is opened and draws a max, of 7 amps --
This has been quite addaquate, but when takeing a shower, pressure drops a little, if another valve is opened, but not much !!
I would not recommend using this pump for your circulator, as I don,t think it is a constant duty type -- But, I wonder if you need a circulator, constantly !!??
I would think you would only need to circulate water, once or twice a day, and would put that on a timer -- even if this is a part of a purification unit !!
My tank, sits, often for several weeks or months, and I have had no problem with water purity -- as i filter it before it goes into the tank, and again as it comes out ..
In a home, where it is used constantly, i wouldn,t think that circulator was necessary-- unless, this is a cistern, and not filled from a well !!
At any rate, as Ghurd pointed out -- look in the Granger and Northern tool catalogs -- or just drop by a RV supply store -- but, compare prices, and another thought, is Ebay -- As I bought one pump thru them !!
Let us know how it goes, Bill H......