First we have to see whether RCT is or isn't a viable option for treatment in your case. To do that, we have to take an IOPA (radiograph) of your tooth, and check for the reason behind the ache. Also we have to look at the supporting bone structure to check if there is any bone resorption or not. We also have to look for presence of any abcess or pus on the region. Only by looking at all these factors, can we take an informed decision on whether we can do an RCT or not. Now having said that, RCT is still the best chance of saving your teeth (where it is applicable). As to your query, the way it works is first, we open the tooth and remove the infected pulp tissue from the root canals. Then we fill up the canals with a material known as gutta percha, and fill the remaining tooth with a filling material like a cement or composite. Then we prepare the tooth for crown placement and finally cover it up with a crown. Now the charges of the crown varies according to the material and procedure used for making the crown. Depending on that it can cost anywhere around 1k to 20k. The cost and longevity of the crown will ultimately depend on your affordability. It's like buying a smartphone. You can get a samsung s8 for 50k, but also get a mobile for 5k which essentially has the same functionality, but at a lower quality.So my advice would be to discuss it with your dentist before the treatment. Hope this satisfies your query.
Next Steps
Consult a dentist, and get an IOPA taken to plan the RCT.
Health Tips
In the meantime, you can take Mox CV, and Paindrop SP twice daily after food for next 3 days, and take Somi DSR twice daily half an hour before food for the next 3 days. Also, do not delay, as it will allow the infection to spread, and if it spreads too much then we might not be able to save the tooth.