Graduate students. Graduate students, as much as I hate to say this (being one) can be bribed with paper authorships and the like in lieu of actual money. It's important to recognize that said project may get done a little more slowly, as it won't be their first priority if they're also doing something for funding.
Some academic departments also have consulting classes to teach their students future skills needed to be, well, consultants, or practical experience requirements that mean students may be looking for projects. There's also always the possibility of framing your project as a potential masters thesis or the like.
So lots of ways to potentially get free/cheap labor from graduate students. The best place to start is probably emailing the department secretaries of departments from Universities near you with the kind of student you're looking for.