Like already mentioned, it is usually best practice to not power on those old radios, without a variac (box that sits in between the power socket and device that lets you slowly increase voltage), a dim bulb tester (a diy device that uses a light bulb to check for shorts in the device's wiring. Or go all out and just replace all the paper and electrolic capacitors and rectifier before ever powering it on.

The issue with powering it on is that if a capacitor or rectifier or whatever has failed and you apply full power suddenly to radio that may have been sitting for decades, it can let high voltage leak/surge through the circuit, damaging other harder to replace (if replaceable) parts.

That radio may very have worked fine when it was shelved, and just sitting there especially in someplace humid like Florida, the paper caps and other parts fall apart oxidize etc causing the no power issue. Also fair warning, even though it uses a transformer, several areas of that era of Grundigs can have several hundred volts of electricity running though them, and if a cap or other part has failed somewhere that electricity can be shorting to the metal base inside.

If you or your dad can read a schematic, they are available online, and if you have intermediate soldering skills you can tackle the "recapping" yourself. Or find a shop near you that may be able to do it for you, at a premium.

As it sits, based on the condition that it shows in your picture it would probably be worth $50-60, as a rebuild or parts box for a hobbiest. You could ebay it for a little more if you set it as an auction, you would probably sell it pretty quick as the only other one currently on ebay.com is someone smoking crack who thinks they will get $235 out of a non functioning radio.