If the root canal is done properly you should never have any problems with it. Most dentists send you to a specialist that only does root canals. Contact who is going to be doing the work, explain your situation and ask if you can setup a payment plan with them. A lot of dentists will work with you. Till then, I would rinse with peroxide daily. The peroxide will kill the nerves and keep the tooth from getting infected, just don't drink it.