Clear Drain from Toilet to Street
As others have suggested, knowing why it backs up is key. 
For that, a reputable plumber with a camera can find the absolute answer. If it's damaged pipes there is no other long term option than replacing the main. 
If it's backing up due to bends or joints then installing a cleanout would be the best option for cleaning it out yourself in the future. Then you could buy your own sewer machine (I've seen them as low as $150 on CL) and deal with it yourself. With a cleanout installed you could also have a service plumber clean out the line for about $85-$100 per visit in the future. 

Alternatively, you can add products to the line yourself to maintain it, things like a lye-based gel or heavy duty main line cleaners such as Liquid Plumber, to keep some of the solids or semi-solids from accumulating to the point of backing up the line in the first place.

Lastly, have you checked to see if the local sewer/water company offers main line insurance? Here at my house it's like $10 a month and covers main line failures. After signing up it would be wise to wait at least a month or two before filing a claim on that.

Good luck!