I have put together a price list for you based on what you said you would need:

Apex Jr

This comes with NET already, but does not come with PH or Orp probe inputs. You can add these by adding a PM1 module to the system.

Base unit - 149.95
PM1 - $74.95
Total - $224.90

RK Lite Base

This does not come with NET or PH/ORP inputs. You can add a NET module and a SL1 module to get this functionality. So...

Base unit - $119.99
SL1 - $60
NET - $115
Total - $294.99

RK Lite Plus

This is the next step up in the RK Lite and it does come with the SL1, but not the NET module. So if you add this...

Base unit - $279.99
NET - $115
Total - $394.99

RK Lite Net

This comes with the SL1 and the NET module.

Total - $379.99

So for what you want, I think you get the most bang for your buck with the Apex Jr. Hope that helps!