Here's a link to a blog I wrote on how to find lease-to-own properties: http://bit.ly/findaleaseoption
However, I agree with Jim about the risks of a large option fee. (Note: It's not a down payment. You lose it if you don't exercise the option.) Typically, an option fee is 2%-4% of the value of the property. You should almost never consider more--certainly not the equivalent of a "substantial down payment." Frankly, your goal should be to provide as little up-front option money as possible. Please read up more on how to properly structure lease-options.
Hope that helps.