cooking propane lasts a long time

We finally used up one of our two propane cylinders after four months of heavy winter use. This is with a little 4 gallon standard sized tank like many grills use. We cook nearly every night, sometimes two dinners since Paul is on a different schedule than us, plus we have baked fairly frequently. We were considering renting a 90 gallon "pig" for $6 a month, but even that might not be needed since we might only use about two little tanks a year, and they're easy to fill right down the road.