Have sewerage under my house and the fumes are coming up into my home. I have COPD and the quality of air now is poor and I can't afford the repair. Where do I turn

First you have to stop using it, if you keep using it, it is going to get worst and worst, Even causing you health issues in the house. Also by codes this waste may have to be removed, which is going to add more cost.

But check Craigslist or other such things, for "handy man" who may be cheaper than a plumber. Or some plumbers large companies may have a finance plan