I've never really thought much about shopping around for an x-ray, ultrasound or CT scan. But it turns out that being a proactive consumer can make a difference. 

Sometimes insurance companies will try to sway patients with respect to where they have their test done. The rationale is that the patient will pay less toward his or her deductible at certain facilities -- and that also means the insurance company will pay less for the procedure. What isn't stated is that the quality of the equipment used at a facility that charges less may not produce the best scan for the radiologist to read, which can lead to a retest (more money out of the patient's pocket) or a missed diagnosis.

 abdominal aortic CT angiogram taken with a 4-slice machine (lower quality)

 abdominal aortic CT angiogram taken with a 64-slice machine (higher quality)

Where you get your scan can also impact the access your physician has to the image. Community imaging centers are electronically integrated, so network physicians have direct access to the images. They can compare scans that have been taken over time to identify any changes that may have occurred, and they can have the image on-screen during a procedure in the operating room.
 
It's worth investigating why you may pay less at one imaging center over another. There may be an important reason!