Least expensive method to buy bitcoin.

I’m brand new to crypto. I’m interested in acquiring some bitcoin for my children. I will more than likely a buy and hold strategy and after reasonably large initial purchase, I might DEA a small amount of money every month. I am really hoping to avoid as many as possible. Can somebody help me out and suggest an exchange and storage method to get as close to 0% fees as possible? I tried to open up a STRIKE account but it’s been “under review “forever, so I’ve lost faith and strike. Thank you so much for any help.