I'm not some kind of grill master who knows everything about propane grills, but I do know that I've generally paid $20 or more for propane ever since I found the grill out in Delafield near my in-laws house. I believe Menard's was around $18 when I was back in Wisconsin and Kansas, so that's a decent deal, especially since half the gas stations charge $22. You might be able to use your 11% off at Menard's, too, so that would bring it down to around $16. However, I'm not positive the propane tanks are still $18 at Menard's because I live in Florida now, and I have to put up with Home Depot and Lowe's.
In my area, I have found that the best deal on propane is at Family Dollar. Technically, they charge $20 even, which is a penny more than some other places in the area. However, I get a $5 off $25 coupon almost every week in the mail, so that makes my propane $15, as long as I buy some unhealthy food to go with the exchange. I bet most people throw their coupons away, not thinking there's $25 worth of stuff they'd want at Family Dollar (especially since you can't use the coupon on booze), but keep propane in mind if you get one of those coupons, folks.