Knights would be rich as to be a knight, a king/queen will have given the knight or much more likely their family in the past the title and land which they would lease out to farmers. Lots of armour was passed down and refitted the knight would generally do 40 days service to the king/queen per year (gaining favour would come with the possible chance of new titles and land etc) The knight would also need a horse, squire (knight in training) and various other staff to fulfil his duties. There was also sports events that would bring in cash, popularity and maybe a rich bride with a dowry too