I did forget water filters Valterra adjustable is the lowest I'd consider
I used both a Watts and when it wore out a zurin (Since I could not find a rebuild kit) both were about 50-60 bucks with hose adapters. both were 3/4" (turns out 1/2 inch is more expensive???) went from static (set to 50 psi) to shower at full flow (Still 50 PSI) and the pressure gauge on the output looked glued in place (it was not) The elcheapo jobs that gauge dropped like a rock in freefall.
The three things you need the most
Master Card
Visa
Checkbook