I have 3 used French horns that have been fully serviced and are in excellent playing condition.
First, the King double ($700 obo) is a solid horn with smooth and clear tone close to that of a Yamaha. There is quite a bit of lacquer rash but it plays perfectly well. Hence the low price. Vintage King double horns sell online between $1000 and $2000 (pics 1-3).
Second, a Yamaha single YFR-314 that retails $2800 new (see http://www.musiciansfriend.com/brass-instruments/yamaha-yhr-314ii-student-f-french-horn) again with quite a few signs of used but serviced and playing without issues. Asking $600 obo (Pics 4-6).
Third, a Huttl (German made) single in excellent playing condition and with some lacquer rash. Asking $500 obo (pics 7-8).