What i've seen in the past, is people building simple clickable-prototypes using something like InVisionApp or even using Keynote presentation software + http://keynotopia.com/ to build clickable demos within that. Hiring programmers to build out your prototype is tough since the low-cost will get you developers with not enough experience knowing how to build "just enough". And hiring expensive ass developers will get you a project that blows through your budget just coming up with a style-guide.

How we usually help people in your position is: build a very quick proposal of work done with time + cost, and then see what its going to take to get you in front of people to get more money to finish the build-out. It's just like buying a house: you can't get a mortgage unless you put a little something in first, to get the bank to help fund the rest of it.