Looking to have relay operation stay until XX condition is met.

(deleted)

Please post your program here rather than in another website.

You have almost answered your own question in your title. If you have a variable (let's call it conditionMet) and start with it set to false. Then when the desired value arises change it to true. Your code could then be something like this pseudo code

void loop() {
   if (conditionMet == false) {
       turn relay ON
   }
   else {
       turn relay OFF
   }

   if ( waterCost >= threshold) {
     conditionMet = true;
   }
}

You can probably figure out a better name than conditionMet. I just used it to link with your Title.

...R

(deleted)

(deleted)

For the future, if a program is too large to include then just add the .ino file as an attachment.

...R