I have been living in my house since 1974 and have not had a drain problem until March of 2011 when my drain and toilet in the basement backed up. I called a plumber and they snaked out the pipe to the main they said they went out 150 feet (it is only 52 feet to the main) and could not unblock the pipe so the used a water jet snake which cleared the pipe.
In May and until November the city did my street and put in new sewer mains along with the last 30 feet of pipe from my house to the main. In December the drain and toilet backed up again. I again had the plumber jet it out and had the city inspect the main I also had the pipe inspected by the plumber using a camera, the city also inspected the main with their camera and both saw no problems.

I have now 10 months later had the problem again. I used a 75 foot power snake to try to unclog the drain but it did not work.
What other options do I have I do not want to have to pay $400 every year to unclog my pipes.

I notice you never mentioned doing anything with your vent stack... has that ever been checked or snaked yet?

Since the jet couldn't bring anything back I suspect a root problem and I'll bet they will be found at the city raiser, (the connection at the curb between the city main and your sewer.).
You could dig up the line looking but a easier fix would be to simply kill them.
If you wish to control roots RootX or Robics Foaming Root Killer that contain Dichlobrnic are two products you could try.
A less expensive way would be to call around to garden supply stores and ask for fine grain Copper Sulphate. Put a 1/2 pound in your toilet and flush it down. Repeat in 6 months.
Hope this helps and thank you for rating my answer, Tom