Most shoes will last for 400 to 500 miles. It's a good idea to rotate two pairs of the same or similar training shoes. This will allow wet shoes to dry before you need to wear them again and save you a few trips to the running store. Not all injuries are caused by shoes, and new shoes won t instantly cure an existing injury. A correct new shoe model may remove the cause of the injury, so that the body can heal itself.
New shoes can t compensate for overtraining.
You get what you pay for. What you don't pay for now, you will probably pay for later. By the same token, the most expensive shoe isn't always the best one for you. Most of the time, a few ounces really don't matter. Lightweight trainers and racing flats work best for people with efficient biomechanics.