It is tough to say without a detailed inspection.
There are a lot of potential costs like:
- rebuild engine
- rebuild transmission with new clutch
- wiring harnesses might need repair or replacement
- new brakes
- new brake/fuel lines
- new tires
- old body damage surprises
All in addition to the paint, interior, known rust issues.
It is a super cool car and desirable. I am thinking closer to $15k
You will have over $30k into it when nicely done. And that is close to market value.
1965 Mustang 2+2
1968 Mustang California Special