The National Living Donor Assistance Center is the premier source. I filled out the application but the social worker at our transplant center intially told me it was only for people traveling great distances, which is not true. I asked her to sign off on it, and I was approved. We only live 30 miles south of our transplant facility. It's for ALL donors!
https://www.livingdonorassistance.org/They have a formula for calculating your mileage to the hospital, they will provide for meals, gas, money for a companion, lodging, etc. They are also well funded from national grants.
When I donated, I was allowed to fly my sister here to Mass. from Washington D.C. to help take care of me. I couldn't walk, I was bent over from the incision and I couldn't even perform basic hygiene tasks. I WAS SO GRATEFUL for her being here! I couldn't have done it without the assistance of the NLDAC.
They fund an American Express credit card with your budget and it is active for up to three years. It covers follow up visits and any visits related to the initial donation. The team is also very supportive and they make sure you have resources for what you need. It made a big difference.
Good luck!