Great question. I have spent 15 years in the seed stage startups and now is a great time to be building and funding a mobile startup. We (my seed VC fund) invest in a lot of mobile startups that are pre revenue. Typically in the range of $50,000 for 5%.
That being said, having an MVP isn't enough. First try to bootstrap your way to early users. Customers are better than investors for a variety of reasons, including: no dilution and access to user feedback. Then try kickstarter, especially if this is a b2c app. Nothing proves you have a hot product like early users, especially those early users willing to put their money in first.
Next I might turn to an accelerator like Techstars or DreamIT. This programs offer you way more than just cash. These programs offer: mentorship, education and buzz. All very helpful assets in the early days.
Hope that helps, drop me a line if you wish to know more.