Rodney,
I have several 66-16s and -18s as well as several earlier models. They are, in my not so humble opinion, Singers best straight stitch machines. Easy to use, easy to maintain and they use common bobbins, needles and accessories.
I wouldn't try to pry the 101 from your daughter. Let her bounce from one to the other and decide which she likes as you service them.
Nor would I worry about the price of the slide plate. No, it's not cheep, but it's a one time expense that if you pay attention to how it works won't be going anywhere.
Joe