What is the problem with locks on 2003 Eurovan and probable repair costs?

It sounds like it could be a couple different things. I just had to replace the outside drivers door handle. The level on the inside of the door handle is made of pot metal and it had just broke. Easy to check just remove the two screw located in the door jam across from the door handle and see if it's broken off or not. I went on line to partstrain.com and purchased one for $136 free shipping no tax. If the pot metal is not broke and the door panel is removed you'll see a metal bar that the inside door handle moves to open, this same bar is moved by the outside door handle to open. This bar is held in place by a plastic fitting that holds or snaps the rod into a whole you'll see when you remove the outside door handle. If it is neither of these possibilites it could have to do with the auto lock electronics where when you lock the drivers door with the key it auto locks all doors Hope this helps good luck

Possible drivers door lock actuator , or signal to it is faulty. Testing would be best.

check the wires where they go from the body to the door. from constant bending ie. door open-closing they break . [may not be visable] inside the plastic insulation. bend they to feel if broken inside. start with driver door as all are connected from there. then pass.and all others. repair.