Sayyiduna Ali (may Allah be pleased with him) fixed one dinar (as the reward) for a runaway slave, whether he is found near or far.
And it is narrated from Amr bin Shu'ayb that Sa'id bin al-Musayyib (may Allah have mercy on him) used to say the same.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب اللقطة / 12124