There's a magic number of job applications necessary to land the job. I can't tell you what that number is, so you have to keep doing it.

And what I would do, rather than use the offer as leverage for a raise is to leave. I would leave them in very good shape, documents for everything, knowledge transfers to my successor and be available for some consults after I leave, etc. I would be the good guy. For me. I need to like my reflection in the mirror.

They are unable or unwilling to pay more now. That won't change if I put a gun to their head and force a raise out of them. Other things will however change, and that is highly unpredictable, but probably mostly in the column of I'm fucked rather than they're peachy and happy with the situation.