If you want the best, you won't beat RCPlanebuyer for 9mm SS grates and 16 gauge flavorizer bars. But you will pay for them to the tune of about $200. But if you are looking for something lower priced, I have no problem with a lot of the after market parts. A good set of 7mm stainless grates will last you longer than the grill will last. And there are several offering for 16 gauge 304 stainless flavorizer bars (which is what RCP offers) for very reasonable prices including shipping. I have a $13 set of burners on my personal Genesis 1000 for 4 years now and they are still going strong. But I also have a set of RCP grates and flavorizer bars.
So, if you want the best, get the RCP grates and flavorizer bars and grates and weber burners. Cost over $250.
If you want a step down but still very good parts, you can get all three aftermarket for about $100.
For grates, these SS 7mm will cost you about $30 shipped with the 10% off coupon:
https://www.amazon.com/gp/product/B083QPHF5N/?tag=tvwb-20
For flavorizer bars, these 16 gauge set will cost you under $25 shipped:
https://www.amazon.com/gp/product/B07SR9KHKR/?tag=tvwb-20
For burners, you can get these for under $10 shipped:
https://www.amazon.com/gp/product/B07RLXLWYR/?tag=tvwb-20
That would put all new SS parts in your grill for about $65 shipped to your door step.