You could try using a drain cleaner but if the blockage is due to inappropriate items being flushed down or even tree roots etc (if it is a stand alone house) getting into the sewer pipe, then this won't be of much help. An electric eel which all good plumbers have will be required to unblock it.
If you are renting the premises.
Call the landlord (or agent) and ask if he/she will arrange and pay for the repair. After all it is in their interest as well that 'their' property remains in a good condition. They may say that it is your responsibility but they also just might do it on the understanding that if the problem can be traced to tree roots etc then obviously it is outside of your control and they will pay for it. If it is found however that it was due to disposal of inappropriate items then it would be down to you, unless you can convince them that you do not do that sort of thing. Then they may relent and say that if it happens again it will be down to you. Not all landlords are uncaring regarding their tenants. Ask them nicely, you might be surprised. You have got nothing to lose, at best they will fix it and at worst they will say no, your problem. Then again you know your landlord better than me.
If you own the premises
Then call a plumber. I realize that you say that you cannot afford one but what price good health. You might find one who will do it on an installment payment plan. After all they know where you live.