Automotive question about new tires?

Hi everyone. I bought a Scion XD and is great. However the dealership of course is a rip off when it comes to buying tires. I have almost 30,000 miles on the car and was told I need to get new tires soon because it is close to the reccomended tire tread for new tires. Ok. It seems that the size of the tire is rare, difficult to find at a reasonable price, quite costly at least for this retired grandma!! They want 650.00 to replace all 4 tires and I looked it up and the tire is a bridgestone turanza 400 el which is not anything special. Are there any mechanics out there or tire people who know how I can get a decent set of tires in that size put on for 450.00 or less? I know there are some decent tires out there at least as good if not better than what the dealer is telling me but the problem is the size. It takes 195/60/16 and I looked it up to find that the 16 is the rim size. Is it possible to get a 195/60/15 that will work without any damage or problems for the car? Any advice here would be greatly appreciated. I am on a fixed retirement income and cannot afford that price. Oh yes, on top of that they want to charge me 374.00 to have regional required maitenance done which includes complete fuel system treatment (stuff they just add to the engine I think) fuel induction service to correct injector spray?? If needed. If not I still have to pay for this. Brake check which they just did at 25K miles and tire rotation which I don't think will be needed if getting new tires. The car is not even at 30K miles, is all of this really required??? Thanks much.