In the US, you may get a fair bit of information from the biennial reports of the Bureau of Labor Statistics for various states. For 1899, the telegraph operators in Colorado, where it was still very important, made on average around $825 yearly as against a cost of living averaging around $500. Wages would have varied by state, region (rural/urban), and employer, as those figures suggest. You can make a comparison on the wage end with Michigan in 1885, but you'll have to adjust for inflation; the relationship to cost of living was not too radically different. I'm not sure where Express riders' pay would be recorded, especially because it operated for such a limited period.

I'll see if I can find any better breakdown of this position, especially for the early establishments. I can find South African data, almost certainly, but that may not be too helpful.