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.
GrapheneOS team is helping Motorola build secure phones to spec. but Motorola won't have some special bloated flavor of GrapheneOS installed
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
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.