If you are just looking for normal tires and know that you need them, call ahead and get an "installed" price from Firestone, Discount Tire, NTB, etc. If you are looking for specialty tires that are harder to find, then your options are more limited.
FWIW, I get tires from Firestone. Then get the lifetime road hazard/rotate/balance for $10 or $15 per tire. Then you can make an appointment for when you need an oil change and get the oil changed and then tires rotated and balanced for free. Makes it convenient to rotate on a regular basis and extend the life of the tires.
Been doing that with our three cars for a while now. Works pretty well, as I like that they do appt's for oil changes. If you need other work done, you can decide to do it at Firestone or take it elsewhere.