The kits can yield a nice instrument at a decent price, but you should factor in the value of your time. There's a LOT of work involved in making an instrument from a kit. IMHO, it doesn't make sense to buy a kit simply to "save money".
I personally like the Kentucky KM-150 and (especially) the KM-160s, though I acknowledge that they're more than twice your intended "$100" price point. I don't have any personal experience with the Rovers, so I'm not in a position to comment. That said, Saga has a very good (and. IMHO, deserved) reputation for making quality instruments.
I'm always on the lookout for decent low-cost mandolins that I can loan to my students/friends, but finding good deals in used instruments takes a lot of time, effort, and knowledge of what to look for.
I second the suggestion of keeping an eye on the Cafe Classifieds.
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