Fundraising happens at every level, including D1. And the answer varies by team and program needs / desires.
Could be for expenses related to the team's Spring break trip. Maybe it's a capital campaign for a new scoreboard. I've seen anything and everything at both D1 and D3.
Many programs will do a kickoff event in the late Winter to raise expense $ for that coming season. Dinner, silent and live auctions, special speaker, etc.
Some programs will do a direct ask...we want $XYZ from each player (no obligation of course) to cover miscellaneous expenses for this season.
I wish I could "bound" it, but I can't. We've been asked a floor of $500 so far. The ceiling is whatever they can get.