Two reasons:
1. You're young and still figuring out what you love doing; no better time to experiment and learn. I still have fond memories over the php site I wrote in high school. You could visible tell which functions were written at the beginning of the project versus the end because you'll improve drastically. [1]
2. The project will be more successful with someone who cares for it. Hiring a contractor will make it difficult for you to maintain and improve. Contractors will also expect a specification with penalties if you need to change it. My guess is that you're still experimenting with what can best serve the community so this probably isn't a good fit for contracting as well.
[1] Recommended tech stack (optimizing for documentation and availability of help). Ruby, MongoDB, Heroku (or if ambitious, Linux on Amazon EC2 + nginx). Everything else is pretty similar so once you learn these, the concepts apply reasonably well.
p.s. If money is a concern, you should look into contacting some companies PR/DevRel people and see if they are willing to donate some compute time or services to your cause. (It's probably doing this after launch and getting a better sense of usage and will be easier to convince them that you're legit).