I recently had one of my guitars serviced because its neck was warping, and it was quite pricey (acoustic guitar from 70's - dad gave it to me). Take it to your local guitar shop or music store - they'll tell you if its worth repairing. But at a glance, I expect that you'll pay a lot to get it in perfect condition. Do you aim to play it when you fix it, or sell it? If your goal is to play the guitar, I suggest you just buy a electric guitar from a guitar store (it'll probably be cheaper, but thats my guess).
Repairing guitars in the type of condition you're describing is often rather expensive, similar to if you just want to customize a guitar, the parts can get quite up there in price. The good thing though is in both departments there is often a middle ground. That is you can repair it enough for it to function then top it off later. Given that it's a classic & they don't make them anymore that's what I would recommend. I'm of the mindset that you never give up classic instruments regardless of their state.
I have a red Mann double neck that looks like the one Jimi Page used when playing "Stairway To Heaven", I bought it from a friend of my bro's father. It says made in Japan on the back & I think it's from the 1970's/1980's. The wiring is a bit shot, the tuning pegs are 75% to stiff, the bridge screws for setting intonation are mixed & matched so it's slightly off, the nuts need replacing, & I'll have to take it in to see what condition the pick ups are in. Overall it's guaranteed to be an expensive fix but it is playable & I do play it. One day it'll be prime again, that's my goal
The bridge is supposed to come loose like that. I would think that if you add an output jack, make sure the wiring is solid you will have something playable provided the neck is in good shape. The bridge may still be a problem as you have to set the intonation, maybe take it in for that.
The finish is in a pretty good shape considering the age of the guitar. Seems like the only crucial part that's missing is the jack. Is the pickup switch still there? I can't tell from the pics.
I'm not sure if the bridge is supposed to come off. When the guitar is strung, the strings will keep the bridge in place, but you'll still need to put it in the right place for the guitar to be in tune. The metal thing behind the bridge that holds the strings seems pretty rusty. You might want to replace it with a solid metal thing instead of a largely useless vibrato mechanism.
So looks to me that to get this guitar in a reasonable working condition you'll mainly need to have the electronics and the bridge assembly done (maybe replace the tuners?), clean it up, and have it set up properly. None of that should be very expensive. Sure, it might cost as much as a new guitar, but I'd pick a vintage guitar like that over an el cheapo Ibanez any day of the week.