1847 & 1848 year Pre-philately mail cover:
Like what we know, pre-philately in Serbia start on May 25, 1840 year, when was opened first post station in Belgrade.
Yes -existed mail delivery before this date, but it is carried by horse rider, and mail didn't have cancellation, or cancel alone.
When valuing this kind of envelopes, we need to think/care that envelop have nice readable cancel, good condition, visible date and city name, and to know rarities of cancellation and cancel numbers. For this elements, I prefer one nice and professionally edited catalogue of Serbian Phila Club Beograd (cover period 1840-2003), issued in 2003.
On scan is two cover used in 1847 and 1848 year that are shown here.
Looking on market prices, recently it was offered on eBay, and sold for really bargain prices of 10-20 euros, but when is question about really market value - it can reach also more that few thousand euro, all is conditioned with cancel rarities and from where it is delivered. I can see on SFK catalogue one sample of Aa Beograd post, with date May 25, 1840, that have catalogue value of 12 000 euros and I think it can reach much more if offered by any world class auction.
Just to mention that in Serbia was in use also Turkish Post Service (1841-1878), and "DDSG" (Donau-Dampfschiffahrts-Gesellschaft 1840-1880) and according same Serbian catalogue, envelope with this period cancellation can reach from 300.00 to "open" market value.