Parts are cheap and easy to find for the 27. :)
$35 is a little high for decals in this poor a condition, but the nickle plating appears to be good and I've never seen that face plate before, so I would buy it. :)
You will need to replace all the electrical components - like you said, that will bring your cost up to about $100-120.
The only drawback to the 27/28/127/128 models is that they have a shuttle and long bobbin and if you don't use a bobbin of exactly the right length on the bobbin winder, you will end up with a dog-bone effect.
You can use modern repro bobbins, but they are a tick too short so you will have to guide the thread onto the bobbins with your fingers. No big deal, but it is a bit of a pain in the neck.
It takes ordinary 15x1 needles and standard low shank feet and accessories.
Some people are crazy about these machines for FMQ. :)