Toilet Flange Repair Issue

I could really use some help! I am in the process of replacing a toilet in my downstairs bathroom. Upon removing the old toilet, I discovered that the flange had nearly completely rusted apart. So much so that I could remove it just by pulling it off. It was mounted around a 4" pvc pipe coming out of the concrete slab, on the underside of a kind of funnel of sorts. (I know I'm using the wrong lingo, but I'm trying to learn.) I'm trying to figure out if there is a way to attach a new flange without having to call a plumber out. Money is pretty tight and it would be amazing if I could take care of this myself. I would greatly appreciate any and all information anyone might be willing to share. Also, I'd really like to get this taken care of today since I don't have a usable toilet downstairs right now. Thanks!