I only posted this as another solution so that everyone could find the spreadsheet more easily. I tried to make the spreadsheet as easily accessible and usable. When you get a player that you want, type X in the box (upper case I believe).
This will then show you a few things, how many you have (which allows for checking against the number under the league if you only collect one from each team like I do). And it'll give you a percentage of both that collection and the FINAL collection.
EASE was my biggest concern with this, so I tried my hardest to get all of the abbreviations right, because if you're like me -- you search for the cheapest price across the whole league, but with some of the European leagues its impossible to guess what that teams abbreviation will be.
Okay: Go to this link: https://docs.google.com/spreadsheets/d/1gn7JtBHaHy0DHrAHMEtU...
Now, if you hit Control A twice it'll copy the entire thing (I don't know why you have to hit it twice but you do). Go to your own Google Sheets document and paste it in there (I haven't tried it with Excel, but I assume the formulas would work there too).
Now, when you own a player, put an X next to their team. Happy collection (what a pain in the butt, but still easier than NBA 2K)