How can I improve my graphic design skills without spending a lot of money?

You can visit a public library and spend time with graphic design books and magazines. Learn what seperates great design from just average. Go to lectures, visit art museums and galleries, immerse yourself in the visual arts, not just design. Study design history to see who the greats were and why their work remains classic. Study art history. All of these pursuits will help you become a more visual thinker and that is a quality all good designers possess. Good luck and please let me know of your progress.