Well, I think once you know the brand, model, and year that work for you you can buy online. I think it was Road Runner Sports that had a program where you buy so many pairs, you get one free.
My local running stores give me a 15% discount since DD is a high school runner here in town. If you don't have a teenage cross country runner in your house, I would highly advise you obtain one so you are also eligible for this discount. Worth every penny.
My friend runs with a group that is connected to a local shop and she gets discounts that way.
Shoes can be expensive. My current pair was $125 and does need to be replaced soon. But, I'll buy cheap toilet paper and store brand shampoo, but I will never skimp on running shoes. Injuries suck and take forever to go away, if they actually go away permanently. I am so passionate about investing in the right shoes.