It really deoends on where they think the inflammation and how deep they think it goes. Pentasa is good for surface inflammation, it works like an anti inflammatory and stops the inflammatory process in order to let the damaged cells heal and repair. It works better for ulcerative colitis than Crohns disease as it doesn't heal damage that has occured to the deep tissue layers.
In terms of treatments for inflammatory bowel disease, it is very safe and has less side effects than many of the other treatment options, so it's often where doctors will start because if it doesn't work then you can move on to other things, but if it does work you control the inflammation without too much risk.
I know you say that there isn't a lot showing on the pill cam, but the trick with inflammatory bowel disease is to control it and stop it getting to a severe stage. The earlier it gets caught and controlled the better. Once damage has got to a severe level it becomes difficult to control and can sometimes become irreversible and require surgery.
It is of course a good idea to find out exactly what's causing your problems and I can understand your reluctance to take medication when you don't know exactly what is wrong, but sometimes this is incredibly difficult to pin point and this is why some doctors prefer to take a pro-active approach.
I live in the UK and so don't know much about the costs of different medications, so I can't recommend anything cheaper unfortunately.