2008 Saturn Astra ignition

About a week ago, my key stopped turning off the automatic-setting lights and unlocking the doors when I turned off the car and took the key out. It also left the "key's in the car" chime on when I got out of the car. Plus, the RKE would not lock the cars from outside (either the "old" one or the unused #2 key - both with good batteries, I think.) At first I thought I had RKE code problem, but the technician at the dealership had no problem at all - until I got in to leave, and the chime wouldn't turn off. He just jiggled it, it turned off, and chalked it up to the cold weather. Later that week, the car hesitated to start (battery is new), and the lights, locks, and chime go off only when I jiggle it carefully out. A car friend said it is the key cylinder. Does that sound right? I'm on a tight budget, and I can imagine taking it to the dealer and getting whomped, price-wise. If it sounds like a cylinder, is buying one on-line for about 45 bucks and taking it to a car locksmith (the part on- line says it can be matched to my existing keys) a good way to go? Or is there anything I can do to my lock for cheap before spending anything? What is your diagnosis of these symptoms?