My water line is leaking and needs to be replaced with pex. We will dig the trench, which will be 500 ft in length! Looking for the cost to place the pex.

Call around and get 3 estimates. If you are doing the trench, why not lay the pipe and let a plumber just do the connections?

How big is the pipe ? If developed length is 500', I assume it is at least 1 1/2" pipe. Therefore:

PEX will run you around $2,100.00 ( two 300' rolls )
Two end connectors: $ 180.00
One Brass Coupling: 30.00
Rental Fee for PEX Expander Tool / 1 day: $89.00
Plus Sales Tax where applicable

Labor: You can complete the job by yourself in about 2 hours. The hardest part is the excavation. Once you have the trench ready, why not do it yourself ?

If you hire licensed plumber, he will charge you his full day rate. Call couple of local plumbers and ask them what they charge per day. I doubt licensed plumber will run 500' of pipe and charge you for two hours of labor only.

Also, I suggest you run "tracer wire" with the pipe. That will make your life easier when trying to locate the pipe in the future. Add cost of 520' of copper tracer wire to the overall cost

Hope that helps. Let us know how you did

Milo