As a veterinarian who has practiced in a variety of settings, I'd like to point out that "low cost, high volume" practices (like we may be talking about with the guy mentioned above with the free office visit) often are MORE profitable than higher-priced clinics. Those sorts of clinics often have VERY low overhead due to shabbier facility, less advanced equipment, cheaper drugs, etc. You run people through like cattle, limit yourself to quick/easy procedures, and can make really good money doing it. If you're looking to get rich, the low-cost/high-volume model is great... which goes against the popular belief that those guys are doing it out of the goodness of their hearts. Many owners of your more advanced/high-tech veterinary practices are actually making LESS money than Dr. Cheap - they're just less willing to compromise on their quality of care. Quality medicine costs money.
I'm not necessarily saying that the specific doctor mentioned above is awful - maybe he funds his clinic through other sources and really does offer low costs for the good of the patients/clients (or his costs on the non-shopped fees are way higher than other vets in the area). I've worked in clinics with a $150 spay, though. You CAN'T include pre-anesthetic bloodwork, appropriate premeds, IV catheter, propofol, IV fluids, a sterile instrument pack, sterile gloves/gown, cap/mask, pulse ox/ECG/BP monitoring, dedicated anesthesia assistant, recovery monitoring, pain injection and pain meds to go home at that price. Providing quality care costs money. The $150 clinics are typically telazol induction without a catheter, surgery with only a pulse ox for monitoring, and then placed in the back to recover. It works (usually), but not a level of care that I'm comfortable providing. In my pre-vet days, I didn't see any problem with it and revered the Dr. Cheap I worked for as a god... now I've realized how much of what he did would be considered malpractice and how terrible his level of medicine really was!!
About eight months ago, I left a low-cost clinic and now practice at Banfield.... where our spays are about $350 but include everything that I consider important in a spay. I think we're the ONLY practice in our area that includes all of the items I mentioned as 'quality' above. Sure, many of our clients initially think we're priced ridiculously, but when I educate them on what questions to ask when they're calling around for price quotes (one practice in our area uses the same surgery pack of the entire day's surgeries!), most people actually ask for a sheet of paper and take notes on the questions I suggest asking, then they often end up calling back to schedule with us. Some don't - and that's okay, because at least they know what they're compromising on after I've educated them. I will flat out tell people "If money is your first priority, then yes - you can definitely have this surgery performed cheaper. If you're concerned about the level of care your pet gets, though, then here's a list of things I WOULDN'T be willing to compromise on...." Price comparisons are completely useless unless you're comparing apples vs. apples. There is WAY too much variation in quality of veterinary care to assume that a spay is remotely similar between two practices.