Just as an example,

My girl developed an RI when I first got her. She was about 3 months old, and had symptoms for less than a few days (took her in as soon as I noticed). She needed baytril, which I injected orally for a couple weeks. The antibiotics were about $25, but the whole appointment was over $150. I definitely don't regret taking her in for a full check-up, always better safe than sorry. Your pets are dependent on you for all aspects of their care.

Hope that gives you somewhat on a better idea of RI treatment.