Ideally under 300 USD

If you don't mind going used, a refurbished Pixel 6 pro on amazon is a great offer

Why not get a Pixel? OP 9 Pro has a snapdragon 888, a powerful yet incredibly demanding chip which will lead to overheating and poor battery life. Pixels are known for their custom rom support (where you can flash a custom rom with root access) as well as Graphene OS, ironically the ultimate degoogled android experience.

Price range for used pixels on amazon:

80-120 USD Pixel 4a

90-135 USD Pixel 4a 5g

130-150 USD Pixel 5

130-200 USD Pixel 5a

185-260 USD Pixel 6

210-230 USD Pixel 6a

270-325 USD Pixel 6 pro

You could also get a 7/7 pro, but Best Buy just finished up with a sale for them at 350/600 which is way better than the used market.

Buying the OP 9 Pro would be a huge mistake. If you don't mind a few scratches, the $185 Pixel 6 sounds like way to go, or you can buy the T-mobile variant for cheaper here.

I would get the v60 but this is also an option if you can forgo the SD card slot.