I've started a couple of those kind of startups, you don't get software developer to work for equity until you've got a developed product with traction or outside funding, at which point you don't want to dilute your equity and can afford to pay them. Never in a million years will you get a good software developer to work for free for one of the "ideas" I've seen here.
So here's an idea: Offer : 1) To pay a programmer $xyz per hour, to be paid if terminated short of the destiny. And to pay that much at some specific payday when the success of the project can be measured. State what success means and how to measure. 2) Pay the programmer along the way with a way to capitalize on your already profitable judgement. In other words, special access to your signals and help leveraging that value. 3) Some subsistence along the way...so that, depending on the programmers current financials, s/he can survive a year or two of no other income. All by contract that includes a stipulation that if the performance of you trading calls falls below some threshhold, the programmer is free to stop development. Then depending on how long the development is stopped, the programmer is free to leave with full wages or some kind of payment plan.
It's pretty hard to find a good programmer when I offer them $150 an hour plus full benefits plus options in a company that is already very profitable and the leading firm in our niche. I'm almost always looking for someone and always at least one person short or more depending on how fast I'm growing. You're spoiled for choices when you're a good developer, and what's posted here has a far poorer risk reward ratio than literally dozens of other options that a good developer always has open. All I can say is good luck, and remember the difference between a good developer and just a developer are vast and you're talking the kind of thing where a minor bug wipes out your account in a few minutes vice merely annoying a customer.