Which state should I register my LLC in?

I recently started an online store where I sell a fitness eBook. My product is sent electronically via PDF, therefore I do not deal with shipping. I live in MA, but the state fee for registering an LLC is $520, which is much higher than other states. I'm wondering if I would be able to register my LLC in a different state, since I don't physically work out of an office. I conduct most of my business via smartphone, and can do it all over the country. I spent most of my life living in NH, and will be moving to CO temporarily within the next year, and will be conducting business there as well. My family lives in NH, and I have access to a mailbox there. Any advice?