You can buy the book "How to License Your Million Dollar Idea" by Harvey Reese for a few dollars, you can read it, and then you can follow the suggestions that make the most sense to you. There is no one way to market a product that is not patent-protected -- which, by far, are the vast majority of products -- so you need to learn the marketing ropes yourself. And that's best done by learning from the pros.
Yes, the patent process can be expensive, but I would offer my own advice
1. Find an experience but inexpensive patent attorney - there are many patent attorneys that have a wealth of experience that can be found in smaller patent boutique firms, etc.
2. To get a priority date, perhaps file a less expensive provisional patent application. This affords the inventor a priority date in the US patent office and gives the inventor one year to convert to a regular non-provisional patent application. It is less expensive because the filing fee is reduced $110 instead of $545, but also because the requirements are not as rigid. For example, the provisional application is not required to be filed with a set of claims. However, one note of caution, to obtain a proper priority date, the description requirements of the US patent office need to be met - that is, that your invention is described in such as way to enable one of ordinary skill in the art to practice your invention; and that your best mode is described.
I like the idea of filing a provisional patent application, if you have something written that 1) describes the essence of your invention so that others looking back on your provisional application can say that, yes you did have possession of a novel idea; 2) you must describe how to make and use your invention such that one skilled in your field could read your provisional application and know how to make and use your invention; and 3) if you have a favorite way of implementing or practicing your invention, you must disclose it. If your provisional application does not meet those requirements, then its worth is pretty minimal.
Your best bet, if you are serious, is to find a way to scrape together the money you will need to have a patent attorney draft a regular utility application. However, only a patent attorney who meets with you and gets the details of your situation can give you legal advice.