Although you will have to buy a used phone in order to pay less than 250$, it seems like GrapheneOS is the best solution for that problem. Not optimal, but the best among what we have.
I was thinking the same. But it worries me that these news about Motorola in particular doing shady shit. I was looking forward to the upcoming GrapheneOS/Motorola partnership :(
How about the FairPhone running /e/os (which is de-googled)? You can buy it preinstalled directly from Murena.
Although this is not at your target price point. But /e/os can be used on hundreds of android phones (as opposed to GrapheneOS). So you can probably install it on your current phone
Having no GMS implementation at all or using microG introduces compatibility issues for a lot of proprietary software. GrapheneOS is the only ROM which supports running GMS in an isolated manner, without giving it direct access to privileged system APIs such as geolocation (which is sent to Google just because they can).
The pixel 9a was on offer recently here in Spain for 319€ and that includes 21% tax. At major chain called media markt. That phone is one of the few supported by grapheneos.