Upvote. I have done this on Coinbase. I have recurring daily transactions created for Bitcoin and Ethereum, putting in $5 each. Coinbase charges me $0.15 in fees (3%) for each transaction. I realize that the fees have increased since I set this up, but I guess I'm grandfathered in.
FWIW, I've been lately thinking of adding an extra $2.50 each per day for Litecoin and Bitcoin Cash.
As another poster has pointed out, dollar-cost averaging is your friend.