With that type of ride scenario I think you could be in good shape with any of hardtails in that price range from the big brands. Giant, Trek, Specialized, etc. all are trustworthy. I have heard good things about Polygon, though I have never owned one. I would say at that price range you should be able to get a 1x drivetrain (which you should want).
You said rural area and gravel roads, do you get snow? If so, think about a fat bike. You can get away with a fully rigid fork and the cost is comparable. Look at Framed, Wyatt Cycles, Gravity. They look goofy but they are pretty fun to ride and they absorb a lot of vibration from gravel. Just get one with good tires. The tires make all the difference on fat bikes.