sstack.com which is schneiders saddlery has had the lowest prices of all for me and really good customer service. they helped me decide on my first breeches and tried to find an item for me that was unusual.
State line tack was great when my daughter was showing english. they had everything we ever needed at reasonable prices. not quite as cheap all the time as sstack.com but if you watch the sales you can get screamin' deals and they have the selection, for showing western as well. I got my daughter's english saddle on clearance and sold it two years later for my purchase price in a used tack store. The store put the price on it so I did not know I would get that much but I did not complain!