One is "raise over $13m." How? This is not impossible. There is more investor money looking for home today than ever, I reckon. However, this is not a level playing field. Who you are and who you know and how well will make a big difference. This is probably the wrong place for advice about this strategy.
The second possibility is "what is an easier/cheaper idea, that can later become a payment bank?" This is the HN philosophy, from our founder PG.^" Say you had $13,000. What could you build that would get you customers, impress investors or otherwise put you on a less direct path to what you want? Then, you are pitching "turn this thing into a bank" instead of "start a bank" which is a little easier.
This is hacker news so conventional advice here is take on hard engineering problems, and easy business problems. If this was a forum for business people, it'd be the reverse. There, people would rather take the challenge of raising a large sum but avoid hard engineering challenges. You need to figure out what you are strongest at. Are you the kind of person that can cold call your way I to a 7 or 8 figure investment or the kind of person that can build a product in 2 months that will get you investors or customers that will get you to the next step.
Finally, what you are asking is "how do I succeed at this very hard thing." There are no formulas that are easy and will work for most people.
Read this, pay attention to the bridgehead: http://www.paulgraham.com/ambitious.html