For a DIY project you'll probably need to spend more than $15 to get them in a decent working shape with recabling, new drivers, maybe a new headband. These types of projects are for the love of the hobby, as the drivers inside them are usually rated 2000 ohms and sound worse than anything... if you can even find something powerful enough to run them.
I saw one thread where a guy refurbished a bunch of these super vintage headphones with almost new everything, so they were perfectly functional and very pretty, but then gave them to family and friends as gifts.
That kind of project only lowers the value (for collectors) as original parts are damaged or discarded, but it looked like a really cool idea.
The last time I asked about the price of one of these in a flea market, the guy wanted 60 euros... ... and it was in bad shape....so from my perspective it's not a terrible price, unless German super vintage headphones are worth more than American.... ... just make sure it's not one-of-a-kind-super-rare before you rip it's guts out.
Yeah itd be a very long term project with a lot of research involved on my part, but it would just be for fun i think haha.I think i'll pick it up if its still there when i have some extra money and see what i can do with it, if nothing i end up with some cool headphone history I dont imagine it to be very rare but yeah i'll do some research on it juuuust incase