The two Goodwills I frequent in Baltimore County are very cheap on electronics. Most BBXs have been$5 to $40. I got a 1970s GE AM/FM 9V for the wife at one of the Goodwills for 75 cents, it is a real good tuner. It is pretty rare for them to have anything good though. I went to one this week and no radios at all and just one weird Monkey Wards receiver that had a built in 8 track and a joystick that was a combo fader/balance speaker control. I almost bought it, but I don't really need any more receivers, since I recently kick that habit. It was either 12 or 21 dollars.
Mostly the Goodwill electronics area is full of VCRs, cheapo Speakers and small TVs. Oh and of course all those fad food prep toys like quesadila makers, smoothie or schmore makers, and tea brewers. I go mainly for the Target video game discards they have every so often. The games are $10 mostly.
I have stopped by Salvation Army near here a few times and have never wanted anything or the price was way high or was completely broken, There was one near York, PA that always had some cool random stuff but I never got anything. Mostly old video game stuff though.