A simple foot soldier is not worth much, in fact it would have been cheaper to kill him and loot what he got with him than give him food and quarter for several weeks. Of course, a knight or nobleman is worth taking him as a prisoner, a ransom could make you rich. Some facts (source is Wikipedia, so dont take them for too proven):

Battle of Agincourt:
Winner 400
Loser 8 000

Battle of Crecy:
Winner: up to 1 000
Loser: up to 20 000
(both numbers including soldiers injured in a way that they couldn't take part in further battles)

Battle of Pavia:
Winner: 500
Loser: 12 000

Battle of Bannockburn:
Winner: 4 000
Loser 10 000