Knights would get some of their wealth from looting cities and the dead, also Knights used to pay Lords and Nobles 'Shield Money' and that way they didn't have to join the King's army during a campaign. As well as this there are tourneys which, whilst initially costing a lord in prizes (Another way for a knight to make some money.) and the expenses of setting it up, gains a lot more as lots of people with gold to spend turn up and inject cash into the local economy. Lots of small tourneys were held all year round as it was a way for knights to keep their skills sharp, since they only really needed to serve their lord about 50 days of the year.