In town either of our cars are getting about 20 mpg. In 5000 miles I've used 1000 quarts of gas at a cost of about $625. I just picked up a case of Havoline at less than $1 a quart, Purolator oil filters are $2.50 to $4.00 each, for an oil change cost 30 minutes and about $8 if I'm not using any synthetic. If I change my oil at 3k miles I'm using an extra five quarts and another $8. As I recall the severe duty change interval is 3k miles. But, for some reason, one is supposed to feel guilty about using 0.5% more oil products in an effort to get as many miles as possible out of a vehicle, when one could save 50% to 100% by buying and driving more fuel efficient vehicles.
By driving whatever vehicle you have you've already determined the biggest factor, by far, in oil consumption. Keep it in good condition by changing the oil whenever it needs it, and if you really want to make a statement buy a different vehicle if you're worried about using too much oil.