Service dogs are trained to provide assistance and therapy to various people with disabilities. They can aid in navigation for people who are visually impaired, assist a child who is having a seizure, calm a veteran who suffers from post-traumatic stress disorder (PTSD) and can even dial 911 in the event of an emergency. Many individuals depend on Service dogs to help them live their everyday lives.
According to the ADA, service dogs are individually trained to do work or perform tasks for people with disabilities. Examples of such work or tasks include guiding people who are blind, alerting people who are deaf, pulling a wheelchair, alerting and protecting a person who is having a seizure, reminding a person with mental illness to take prescribed medications, calming a person with Post Traumatic Stress Disorder (PTSD) during an anxiety attack or performing other duties.
Here is link to help you find out more on service dog affordability:
https://www.bankrate.com/personal-finance/how-to-afford-a-service-dog/