This is a prime example of "value confusion" that new collectors have to wrap their heads around.
These are quite obscure stamps, issued for the Russian PO's in Turkish Empire 1868-1879, and are the first ones I've handled. They're not something that dealers see every day.
The catalogue value for this group is only £24. A classic example showing that old doesn't equate to valuable. They're attractive and would be a nice thing to have, but definitely not investment-worthy.