Main Sewer Drain

I have an old house, built in 1947. It is pretty solid construction, brick and plaster. However, every since we moved in here ten years ago, we routinely have to snake our main drain. I even bought a 50 foot snake which usually would clear things up for 6-9 months at a time. Typically I would get straggling roots, and at times some stray paper towel, or some other odd thing (like a dog toy once, wtf?)

That being said, I would really like to avoid laying new pipe as I cannot afford it. Are there any other options I can consider?

Secondly, what is the best way to find a reliable and trustworthy plumber? Those 1-800-Plumber type places I find are five times more expensive than they should be, and I seem to know more than they do (which isn't saying much). I don't mind spending the money for a service from someone I can trust, but I've been hosed a few times already from various skilled trade people.

I've heard of getting a camera down my pipes, which I think would be a good idea just to see what is going on, but the 1-800-plumber place wanted $500 for that service, and a local guy I've used from time to time doesn't do it.

Thanks for any suggestions.