The difference between shaved and un-shaved toyos is about 3 seconds.
You'll find the best pricing through the authorized toyo tires motorsports dealers. These dealers offer shaving.
Everybody else has to buy them from somewhere else and mark them up. Very few tire stores have a tire shaving machine because it's a motorsports thing.
The nearest motorsports dealer is Bryan Shackelford and he can be reached at 480.421.8270