I saw on Lion66six's playthrough that he lost a scout drone and it cost him 30 points.
You can see it here on his mission end screen:
It says "TANKS DESTROYED...............1.......-30". You can see the scout get shot at timestamp 16:30.
I feel the score hit is a bit too high for that tiny scout. Most of the time it won't matter, but if your score was tight, putting them into the line of fire could be more of a liability than they're worth. I think 5 or 10 points is plenty.
The score penalty was set in mind with the combat power the scout drone provides, if used to their full extend of capabilities.
Once you start deploying and using them in skilled way, they are extremely powerful, even thou they themselves can not attack.
A team of correctly used Sniper/Rocketeer/Artillery can take out every enemy once the have a hard to hit, mobile and expendable (if needed) spotter.
The drones will most likely die, once you leave them in plain sight to the enemy. (sometimes parking them between you soldier and the aliens may even safe a live =)).
I was actually considering to increase the score penalty even more, or make them more expensive, since the combat value they hold is immense.