Based on those pictures, the cabinet is absolute trash.

Playfield photo is too small to be useful.

If the boards are good, they may be the only thing of value.

I wouldn't pay more than $250 or so for it, assuming I would strip everything of value and scrap the rest.

As a first machine, this is a huge mistake. Even with your intention in mind, this is too far gone. Also be aware than many people have come and gone with the idea of making a "custom pinball" and almost none of them have the skills and grit to stick with the project, so almost none actually realize their goal.