Or you could go to a reputable dealer who has taken in trades and pick up a good used machine, one that may have some bells and whistles. Several ladies in our guild have had good machines and then trade up to a more sophisicated machine staying with the same dealer.
Perhaps a dealer would give you a good deal in trade for one of the malfunctioning machines you presently have for a much better machine. No need in keeping the one that does not work for you. The one you are presently using could be kept for a back up.
I often swap between two machines depending on which one has on the feet I need, i.e, straight stitch on one, zipper foot on the other. Works for me.
Good luck. Suzanne