You can claim anything you want, and as long as you don't actually want to own any rights, you can publish information about your invention anywhere you like, But know that anyone else is free to take your invention and patent it and claim actual rights to it.
You might consider using a non-dislcosure agreement to keep your invention confidential while you try to raise some venture capital to allow you to protect and produce this invention.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Your intent is unclear...
1) Do you want to commit your idea to the public domain such that anyone is free to use it?
2) Do you want to retain some type of protection or ownership over the idea so that no one else can use it without your permission?
With respect to option 1), you can simply publish your idea in any forum you choose. Just be warned, that once you make a public disclosure, there will be no opportunity to later receive a patent on the idea.
With respect to option 2), there is really no alternative to a patent. While obtaining a patent is expensive, the cost pales in comparison to the cost of actually developing and marketing your idea in to a profitable business venture.
You might want to investigate filing a provisional patent application. A provisional application will provide a record of your idea/invention as of the application date. It will provide some evidence that you developed the idea/invention as of the application date. HOWEVER, the provisional patent application provides you with no substantial or exclusive patent rights. Accordingly, you will not be able to stop anyone else from producing/using your idea/invention. Additionally, the provisional application expires after one year and must be followed within that time by a non-provisional patent application.
The actually filing cost of a provisional application is only $110. It is possible to file a provisional application on your own directly with the US Patent and Trademark Office. However, it would be advisable to use an attorney to review your submission to ensure that the application supplies sufficient details to support a later filed non-provisional application. The attorney fee will likely be many times that actual filing fee.
Many clients file a provisional application so that they can attempt to negotiate with existing businesses to license the idea. However, the bottom line is that unless you are prepared to put up the money to be come a true competitor, many existing business will simply ignore you.
The points made above are good ones. In point of clarification, however. Nobody can file a patent application on an invention that they did not invent, so if you publish the idea, it is not that likely someone could turn around and patent it themselves (and get away with it - but I am sure it has happened).
What you are talking about is a "defensive" publication - which means you are not interested in getting a patent, but by publishing it and putting the idea in the public domain, you keep others from patenting the idea as well (even if they independently come up with the idea). So you do this if you do not want to patent, but you don't want anyone else to patent either to restrict you from practicing your invention.