How do I develop HR policies for a start-up from scratch?

With no budget for hiring a full-time HR person, what is the right way to develop HR policies as my startup grows.

You don't need policies until you're so big that you no longer have tight control over who you're hiring. At that time, you should have plenty of money for HR services...

There are HR freelancers who will answer questions, help you with hire/fire, help you resolve disputes, and interpret the law. Expect to pay between $50 and $150 /hour depending on experience.

Like Jason says, don't bother. Use a freelancer for the really important stuff (employment contracts, advice on the law), but the only HR policy you need as a startup is "don't be a dick". You're small enough to talk and resolve things among yourselves. Policies will just get in the way. Decide things adhoc - you can codify things later when you get larger and chatting is no longer feasible.