Hello, JVC M70 is quite a popular one, most popuoalr version being the AUX /RCA one, least popular being the European DIN version. I seldom see the Japan version (with the knobs on the front). From what I can see they usually go for anything between 200 and 500 European dollars in decent and working condition... But in my modest opinion boomboxes are like modern art, antiques,... They are worth what a fool is willing to pay for it at a given moment...
You may find some asking prices on auction and other seller sites and such, but keep in mind most people selling there put in an asking price based on the others asking prices. Better to be on the lookout for actual selling price.
I m sorry if you expect some precise answer about its current value, I don't think anyone (except for a potential buyer making you an offer) can give you that.