If you want low miles you're going to pay for it (ex. the car on Ebay you referenced). If you plan on regularly driving a GT after purchase, I'd highly suggest patience while looking for a car with 20K miles or more on it. The prices will be well below $275K. 20K+ cars that were properly maintained are nothing to be afraid of in the GT world; plenty of members on this site with well over 20K mileage on their cars you can message for a testimonial.
Despite what most people say/think, there are still really good deals out there. My uncle picked up his second GT for ~$165,000 US 9 months ago. It's by no means top of the heap in the GT world (stock 3 option Canadian spec white car, 40K miles, had minor dash damage from previous owner gluing a nav system to it :thumbsdow ), but it was exactly what he was looking for in a second "driver" GT.
Additionally, if you know you want to have specific "big" mods on your GT, I'd highly suggest finding a car with some/most of the work already done. This will likely save you thousands of dollars, especially if they didn't retain the stock parts (negotiating ammo).