I've contributed to two or three granted patents, and I wrote two applications that are still outstanding. None of them included source. The structure and content of a patent application can be readily understood by reading a few online. If you're at all handy with language, and really know the material, it isn't that hard to write one once you understand what goes in them.
Patent attorneys are pretty expensive, and you shouldn't be surprised at predictions of $50-100k to write the application and see it through the process.