Not enough cash to buy something? Ok, no problem, thanks for letting me know. Can I please have an ok button though so I don't have to RESTART MY GAME?!
General rule: Throw spear at spearmen and in 2 on 1 fights only.
Boss 1: Kick him to death.
Boss 2: From memory, kick him to death as well.
Boss 3: Block his spear attacks with your shield, pick up the dropped spears, and throw them back until he's dead.
Boss 4: Make sure you have a spear, keep walking backwards stabbing him in the face at maximum distance. If you miss, kick him once, back off, and keep stabbing.
Boss 5: I went very aggressive with forward swings that cut off his slow attacks. YMMV.