I would obviously pay them if/once the idea took off, but I don't have the capital to do so now.
What you're asking is tough.
Remember, "you get what you pay for."
If you hire someone really good, this means they must stop working on their own projects, which net them 100% of profits to work on your project.
The harsh reality - The coder you're best served to have, will likely require a >50% share.
Anyone working for little or no share, will likely be a hack.
You might get lucky + find a good coder.
Likely you'll require giving away far more than half your idea to acquire good coder(s).