score:10
According to this inscription on a Pony Express marker only one out of 120 riders was killed in the 19 months. This would mean that the probability of getting killed on this job within a year was 0.5%. Then again - one death isn't anywhere near statistically significant.
I see little reason to doubt these figures that are repeated on many websites. The general tendency seems to be exaggerating the dangers and the achievements - so an inflated death count would have been more likely. The real chances weren't as bad it seems which is apparently why many texts prefer to talk about abstract "dangers" without backing it up with numbers. Nevertheless it was definitely not an easy job.