How much stock to give a short term developer working in exchange for equity?

I recently participated on a team with a developer at a hackathon. The person has their own freelance business, so unlikely to join fulltime later. They expressed interest in helping with my project on contract (which I can't afford) or equity basis. The help would be in terms of basic MVP to get going. The startup is very consumer/sales focused and not tech/software based. I'm early stage with zero-funding, so I'd like to pay in equity, But as this is not about equity between fulltime cofounders, I'm not sure how to approach this. And this is not regular parttime either, it's more of a finite amount to be done upfront. Are there any good rules of thumb, proxies or templates to use in calculating equity-work exchange rate? I am concerned about getting this right in order to prevent equity issues with potential employees or fulltime cofounders (I have none yet) and VC in future.