The first thing to do is to visit a specialized endodontist and get an X ray done. If you are low on budget then i would suggest you to go to a dental school. Though the treatment there will be done by budding dentists but it will be under the strict supervision of experienced doctors. The treatment there is quite cheap or may be free of cost.
Now getting back to the treatment, after Getting an Xray, doctor will have a brief idea that what the treatment modality should be. if the caries is involvind nerves also than temporary filling will be done and teeth will be analysed for few days to look for remineralization and if there is no mineralization seen then RCT is the only choice else s/he will do permanent filling...for more detailed info visit the link....http://www.identalhub.com/articlecategory-root-canal-therapy-17.aspx