These are my sons comments about your question. He has been heavy into cards for about 25 years. I know that the condition of the card is very critical:
Ryan 73 topps (I assume it is topps) books for anywhere from $15-600 depending on condition. The last sentence makes me wonder if it isn't a 74 topps though. Theres a common misconception about a card's year with regard to the stats on the back. If the most current years stats are showing for 1973 then it is a 74 topps not a 73 topps. The year of the card is always 1 year later than the last year stats showing on the back.