You can make a precision rectifier using almost any op-amp, it's a type of circuit, not a type of IC. You can use the OPA342 to make one with only two other components!
As cost is important, I would suggest you forget absolute accuracy and use the simplest circuit possible. Just rectify the CT output with a single diode half-wave rectifier, filter it with a small capacitor and feed the resulting DC to the PIC ADC input. It will not be super accurate but you should still be able to see differences of a few mA in motor current, more than enough to determine the motor state and accommodate different motor types.
If you want it to 'self calibrate' the best you can do without a reference load is average the readings over several seconds of normal (pumping) operation and instead of setting absolute limits for the current, use a percentage change. For example, instead of saying 5A = normal, 1A = runng dry and 10A = overload, say "dry = <(normal - 20%)" and "overload = >(normal + 20%)". As long as you can find a value for 'normal' the other limits adapt around it.
Brian.