As far as 1970 B body AM FMs, I have sold a dozen or so (fully serviced/restored) in the past in the $ 750 - $ 850 range.
I don't even bother buying these anymore to resell because the buy in price is so high now.
Now, you seldom see one priced below $ 1,000 .
You will probably pay $ 500 or more for a non-working unit .
I consider the 70 B AM FM to be the "King' of all Mopar radios , as far as supply/demand .I probably service ten times as many 1970 E body AM FMs as I do the B body , and I get probably ten times as many 68-9 B body AM FMs in this shop than the 70 B body.

Greg