If you are looking for mileage over handling, go with 155/80R13's they are practically indentical in height but narrower. My Metro comes stock with 155/80R13 tires and the previous owner put 175/70R13's on instead.
I just ordered these from Discount Tire and had them price match Tire Rack's price of $41.00 each:
Kumho Solus KR21
Discount Tire has a $50.00 rebate if you use your Discount Tire Car Care Credit Card. With mounting, balancing, and free replacement certificates the total will be like $220.00 after rebate. Just an option...
Hacksaw.