How to make money for a project?

Before anyone says "get a job," I have one. I'm looking for something more. I started writing letters of encouragement to send to a rehab place in my town. They have a handwritten note, some stickers, and a few quotes. It's simple but it was something I thought would help me in that situation and I enjoyed writing and putting it all together. There's a bit more demand for them now so I was wondering if anyone had any idea on how I could make some extra money to devote to doing these. I don't want to ask for donations and I'd get a second job if I could but I'm working full time and going to school even now that it's summer so making a little bit of cash online would help immensely. I don't want the quality of these letters to suffer because of the cost because that defeats the purpose. I've already sold anything I had to sell on ebay so that isn't an option and I don't need a scam like cashcrate. Any advice is appreciated!