If you buy an affordable pruning shear and you want it to have a long life, you need to take care of it properly. Most people clean it after they use it and this is recommended by most manufacturers so cleaning pruning shears often should become a habit. Even if the blades are made of a metal that rusts, you should wash them with soap and water.
If they are made of stainless steel, it will not be a problem if you leave them wet for short periods. After you have removed all the dirt, you should rinse them thoroughly and remove all the excess water.
Some people like to sterilize their pruning shears with isopropyl alcohol or bleach, a practice that will prevent spreading diseases from one plant to another. After it dries, you should oil the blades in order to protect them from deterioration.