All on one card for efficiency (they can figure out where they fit-in):
If you gave me under $50: Don't expect an invitation next time. My edumacateeeoon and accomplishments must not mean very much to you.
If you gave me $50-$100: Thank you very much
If you gave me over $100: Thank you so very much. I hope you had a wonderful time at my party and that the refreshments were to your liking. I look forward to seeing you shortly and wish you the best.