I have been a big user of Pex line as fuel line. Even on my 62 psi 2005 CDI mercedes. My old 1985 300d used all pex lines for both diesel and veg side. I used no hose clamps and the stuff was 30 cents per foot. I heated it with a blow torch and pushed it onto the fittings for a perfect fit that never leaked air.

You sound like you are on a budget. You might consider the pex. Also consider just buying a good greasecar switching valve. You can use just one and loop it and make the second valve the 3 way ball valve the one for the return to tank. That way you only need one three way ball valve. Those are not cheap if you think they were, but they are less than the electric ones.

But first I might add that you start filtering long before you start converting. Two tank conversions are actually cheap and easy compared to a good filtering system. I was atleast 3 vehicle in before I had a truely good filtering system.