If the screen still works, you can try applying a cheap plastic protection film for the time being to at least cover up the damage and get a smooth, even screen surface back.
Personally I’d at least wait until Nothing launches the 4a series and decide afterwards what to do. As you mentioned yourself, a screen repair is rather costly, in particular for already more budget oriented phones, but it might still be the cheapest option in the end.
So far we don’t know any prices of the 4a series, however considering the price explosion for certain components, MSRP will likely be above the 3a launch MSRP.
