It probably depends on why it isn't running. I bought my non-running CB750 for $300. It did not have battery, coils or wires. It also needed all 4 carbs, forks, front caliper, gauges and left and right controls rebuilt.
I am guessing that I have another 5-700 into it, and a bunch of time. But it is almost on the road and will have cost between $800-1200. As well, i sold the highway bars, crash bars, air box, turn signals. passenger pegs and luggage rack on Ebay for $180.
If it is an easy fix it is worth it but if you have a bunch of issues to fix it could get pricey. I have seen lots of running 750's for $800-1200
it needs everything.....all the major service items at least and it could run you $800 easily (good tires are expensive).
There is no mention of title. If it has a clear title I would say it is worth it if you could get it for $200. Without a title run the opposite direction. I have a 77 GS 750 and it has been an expensive proposition to get a title for that bike because most title services regard it as "too new"