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Unfortunately value and 21” don’t go hand in hand. If you want value you’re better off getting 19inch rims. As for one of the best tires for the 21” rims I had the Michelin pilot sport 4S and they are an amazing tire. Low road noise, high levels of traction, good mileage rating too.
The new Pilot Sport All Season 4 looks to improve over the A/S 3+ which I like a lot in a 20 inch size. The 4 is available in staggered 21" sizes.
They aren't inexpensive tires though. That said, as important as tires are, they are worth greasing up the wallet for. Here's a video summary of the AS 3+ and the AS4:
If you don't need all season, the Falken Azenis FK510 seem pretty well reviewed and are a lot cheaper than the Michelins.