I learned this the hard way, but apparently you're supposed to get new running shoes every 500 miles or so. I've been using the same shoes for a few years and my legs and have been hurting lately when I run. I didn't even think it could be my trusty old new balance kicks, but my PT told me to try new shoes. Yep, it was, in fact, all about the shoes.
We all need to save money for our shoes. There are three kinds of shoes (neutral, stability, motion control) and you must be sure you get the right kind. If you haven't done this before, go to a good running store and have the clerk check your feet and watch you walk or jog. Don't go to the mall-type stores for this. Once you've found out a brand/model that works for you, you can use the Internet to look for your shoes at a lower price.
Yep, 400-500 miles is the magic number for replacing your shoes. The basic problem is that the material in your shoes compresses with each step and eventually compresses to the point where they need to be replaced. At 500 miles, I promote my running shoes to be my shoes for non-running activities and I get a new pair for running.
Low platforms may not provide sufficient cushioning. See my comment above on the three types of shoes and going to a good running store.