[specialk22]

It is very difficult to make a proper assessment of a vehicles potential for restoration without looking at it. however with that being said... With the level of visible rust that is present and accounted for you can reasonable assure yourself that you will discover upon close inspection at minimum 25-50% more additional areas of rust related concern. Rust will be your biggest area of concern even if all other parts are included with the purchase. Extensive rust repair jobs can get very expensive and finding donor cars has become a near impossibility. (You can though purchase many of the rustoration parts new.)
The value of these unique vehicles though not as lucrative as it was a couple years ago is still a solid investment if done wisely.
The main appeal for most Porsche enthusiast is to own a drive an early 911. While it is fun to watch the demand for them soar past the 100k mark, many owners would not sale them anyway.
So much of this purchase depends on your END GAME or desired results.
Restore purely for future profits vs Restore for enjoyment, life long project desire etc?
Taking a WILD guess based solely on your description of the vehicle I would guestimate anywhere from 18k-35k. I know that this is a big gap however there are many variable to consider.
hope it works out for you.