I've run into this more than once - cameras catch you constantly, and yeah, even 10 km/h over the limit counts as a violation, no exceptions. I can't give you an exact fine amount because the numbers change and it depends on the region, but it's not huge money - definitely cheaper than an accident. The main thing to know: a letter from traffic police isn't a final judgment. It should have your rights and appeals procedures listed in it.
As for contesting it: cameras can definitely make mistakes, but you need to prove it specifically. If you want to appeal, request the case materials - high-quality photos from the camera, maintenance records for that radar, the measurement protocol. A lot of fines get dismissed precisely because the camera failed inspection or there wasn't enough distance between the road markings. Without these materials, appealing is pointless, but with them you've got a shot.
In practice, people often just pay - it's simpler and faster. But if you're confident the camera could malfunction, it's worth trying. Contact traffic police in writing and ask them to provide all documents related to your case - that's your right.