Stay with a large walker, and also stay away from the 50 series, just too much new electronic gadgets to give trouble. The combine you are getting advice to buy on this thread is the way to go. You will get your 1000 acres cut in a timely manner and have plenty of time in most years to do a 1000 acres of custom work, if you want to.
Don't misunderstand my comments about rotaries, as they have their place, and 99.9% of the US new combine market. However, for the acreage you are cutting, the variety of crops and probably conditions, the walker would be my choice.
One of your conditions for a machine is for it to be reliable through the harvest season. In my experience the Maximizer combines are extremely reliable if they are maintained and start out the harvest season in good shape. We put over 2,000 acres on a 9410 last year, starting with wheat harvest in June and finishing beans and milo in December, and the machine never had a failure. We had tire trouble, but was not the iron's fault. We run it though the dealer this winter and spent $10,000 on it. It has 2,500 separator hours. Last year we spent $6,000. Still cheaper and less headaches operating wise, than a used STS. You will be spending money on maintenance and repair every year, but it will be reliable. Just do it before harvest starts.
For the budget you quoted, $80,000 or even less, you will be able to buy a machine that will serve you well. Don't be afraid to buy one from the midwest. A lot of corn and grain machines back there. The freight is insignificant in the grand scheme of things.