Since you've managed to cobble yourself together a prototype in PHP that people will actually pay for there's a good chance you can take it to the next level, albeit slowly, with a couple books in your lap and a few long days. I suggest you challenge yourself to figure out what is the next step you need help with and figure it out yourself. Unless you are looking at some very unique problem solving chances are you can do this.
Funny story: when I started coding my web app that supports myself and my family I had never created a database or re-usable objects. I ended up with huge pages of procedural PHP code and a primitive denormalized database, because I didn't really know any better. I've managed to scale this old code across two servers, and while it's pretty horrid, making changes and troubleshooting is a breeze because it's all mine.