Not sure about walking trainers but trainers for sports like running need to be fitted by an expert.
There are many running shops that get you to walk/run on a treadmil and record you via a laptop. They can then Identify how you run and which trainers will help correct any pronation you have in you running gait that you may have.
Without this fit you can suffer from shin splints which are very painful and take a long time to heal.
I bought an excellent pair of wallking boots from Millets, they are designed very similar to trainers, and very light on the feet,
That was a couple of years ago, but I think they cost about �35.00.
If you buy 'cross trainers' they are designed for all sorts of activities so would be suitable for walking.
If you are looking to do more rough terrain walking I would suggest buying walking boots from Millets as suggested before. You can buy trainer type walking boots these days which might be more what you are looking for?