Perforce looks free but I had trouble setting it up. In the end I couldn’t connect to it.
I’d give the UE integration plugin for git a go above. It uses a much smaller subset of the git commands (I’m going to keep using commandline for commits and pushes) but it has diffing between blueprints and version history. It’s object-aware, so whether it’s a model or a blueprint or whatever, you can see the old version.
Not sure how it handles deltas but I’ve already turned those off for uassets and umaps.