Not sure a profit share will make much difference. You need a joint venture (i.e a startup) and ongoing relationship for it to work. Most freelance programmers will gladly walk away with your many years of hard work as soon as you stop delivering anything of value.... and there's only so much you can bring to the table in terms of trading logic. System development is mostly testing and refining the logic, something that requires you to access it on-demand. How on-demand and patient will your programmer be when coding takes time? How many chances will the programmer give before he/she loses patience? Unless you have a PhD in economics, quantitative or funds management skills, something that makes dealing with you long term of value and you're both invested in the success of the business financially and legally, there's 95% chance it will fail. I wish you the best of luck though.
Spend time writing something helpful because some very nice people, actually high end architects, previously gave the ranges, and then they reply with this nonsense, knew the world wasn't smart but that's ridiculous. They must want the 'stone soup' method of work!
Asking for someone to code for the possibility of a future pay day is odd. Especially when you add the part about how well your doing well - that raises flags as to why than are you trying to avoid paying for it now, that type of deal may work with a friend but not someone you don't already have a relationship with - I could think of about 100 things that could go wrong with the type of arrangement you are looking for - both sides would need a lawyer.
profit sharing is insufficient. it has to be a salary +profit sharing.. it sounds like you need a group of traders to finance this project.
Why would you that? In order to learn that your algo is not working anymore after 60 days and rewrite everything from scratch? :=) Don´t waste your money.