I'm reading The Archers Tale(Harlequin for my European friends), and it told of how some knights were penniless, and had to improvise helmets with old pots with eye holes cut out. I'm curious to know if this is true or not.
Not in the least. There were plenty of soldiers in the Hundred Years War who could not afford heavy armor, but these men would either serve as archers without it or not take a military contract at all. The idea of cutting a hole in a cooking pot is patently absurd: it wouldn't fit on your head or be very protective at all. Someone who could not afford to equip themselves with at least the basic gear of their role would probably not be fighting in the first place.
Bernard Cornwell can be entertaining, but he sensationalizes and invents pure tripe because it sounds cool. Take anything in his fiction with a huge grain of salt.
His Sharpe series exhibits this perfectly. They're cool reads, but follow the exact same formula every single time, and are littered with all sorts of factual errors.