Right HMI/PLC Combo for small fluid metering - all weather

Looking for low cost, reliable fluid metering control system that can be adapted to 12V vehicle system. HMI needs to be all climate with no more than 2 lines, PLC should be able to manage up to 8 inputs and 6 relay controls.

System components/description include:

System voltage: 12V

Flow Meter 1: Main Fluid flow rate signal to PLC

Flow Meter 2: Optional Secondary Main Fluid flow rate signal to PLC

Flow Meter 3: Injected Fluid flow rate signal to PLC (based on Total Main Fluid flow rate)

Servo Control: PLC output signal to Servomotor driven pump or Servo metering valve

Pump 1: For Main Fluid. Independent of injection fluid metering system. Control Note: Injection system only active if Pump 1 is engaged.

Pump 2: SPNO switch closes to send Injection Fluid flow "ready" signal to PLC. Control Note: Flow metering feedback should manage programmed volume ratios during Pump 2 "active" period. Signal lights/alarms for low, normal and high mix should be activated during active period.

Any recommendations on the HMI/PLC combo would be appreciated. Robust, cost efficient, with simple programming (remember I'm an ME) and long term (5 to 10 years) servicabilty are some targets.

Thanks in advance for your thoughts.