You could buy a Janome Sew Mini. Adults even use these small machines. Watch Hancock Fabrics as they are on sale quite often for $49.99, even a couple of times a year they are $39.99. There are some other Janome's at Hancock Fabrics for roughly $89. on sale. They thread easy and are great for young sewers. Stay away from the more inexpensive Brother machines unless you try them. I have compared them, they are difficult to thread and don't run the smoothest.
And like someone else said, Janome makes Sears so they may have a comparable model...