Folding cameras can be extremely cheap, some as low as 20$ or lower. However depending on where you got the camera from they can have issues that were never addressed.
Torn or Worn Bellows
One of the most common issues is torn or worn bellows. Most minor damages with the bellows can easily be addressed with either black electrical or painters tape from the inside. Damaged bellows can either cause the film not to come out at all, or at the very least cause fogging on the film due to light leaks. To check for light leaks you can easily take a flash light and put it to the back of the camera where the film is normally loaded in a dark room and shine it around to see if any light escapes out of the bellows. Typically the damage will be at the corners of the bellows due to usage.
Fungi or other growths.
While I've had the luck of not running into a folding camera with a lot of fungal growth it does happen, especially if the camera was sitting in someone's attic for a few decades in less than perfect humidity conditions. Minor fungal growth won't affect the image too much and can be fixed by soaking in a little bit of rubbing alcohol (99.99%) before rubbing off the surface. Heavier infestation may require a repair shop to clean up or least get to 'ok' condition.
Stuck or slow shutters.
Most old cameras at one point of time or another will get this, often times losing either the slow shutters or the high speed shutter settings, rarely will you get a camera that's slow or stuck in the middle and fine on the low and high ends. One of the biggest culprits to this is inactivity. A camera that has been sitting on the shelf for 40 years has a higher chance of having a stuck shutter than one that was constantly used for 40 years. However a highly active shutter can over time collect dust, and metal pieces from long time of metal-on-metal action. As such may require some cleaning and lubrication. Some people use temporary remedies of using lighter fluid or kerosene to fix the shutter. Sometimes works, but not always. But under no circumstances do you ever want to use other lubricants as most are Teflon-based and can possibly make your shutter fire insanely fast on every speed setting.
Getting Serviced
To get a film camera serviced is often called getting it CLAed. This is to say that it is getting Cleaned, Lubricated, and Aligned. Your best chance is to see if there are local shops or repair centers in your area that can give you a CLA quote on a particular model or type of camera. Sometimes they can go for around 50$ to 80$ depending on who you talk to. One guy that repairs folding cameras exclusively in his spare time is located at Certo6.com, while he quotes higher than a place local to me; he appears to be very experienced in the task. There are plenty of other places you need only Google them. One thing he does do that I might have done is a bellow replacement. My wife has wanted to get the Kodak in a green color.
