13€.
Over the years, I've developed as simple system fro lengthening the life of wiper blades.
When I wash the car, I also wash the wiper blades. Lift them off the screen and using an old face washer, soaked in detergent, I slide it along the blade rubber. The washer will come away black, but the blades will wipe the screen efficiently. This method also removes any small pieces of grit stuck on the rubber, before they damage it.
You can use method instead of detergent.
Then, when the blades do need replacing, I never hesitate. One of my pet hates is getting in a car on a rainy night with a smeared and blurry screen.