I've navigated the USPO site and find its easy for a novice like me to screw up and ruin my patent.
Filing for and obtaining a pantent can be very complicated -- but it is also successfully done by individuals all of the time, it just takes a lot or patience and self-study to learn how to do it right.
How much will an attorney typically charge to prepare a patent.
A patent attorney is generally (but not always) more expensive than a patent agent. Either one can file for a patent, or provide a patentability opinion. If you want more advice beyond simply the patent itself, you'll need to go with a lawyer. But for just filing a patent, and agent is perfectly adequate and usually cheaper.
As far as how much, that will depend on the nature of the invention, how complicated it is, and the location of the person with whom you work. If you live in a major metropolitan area, and want to go with a local agent, it will likely be more expensive than if you go with an agent in a cheaper area. You can work with an agent in another state if you want.
If you do it yourself, the fees alone (for the entire process) can also vary considerably. You can view the current USPTO fee schedule here:
http://www.uspto.gov/go/fees/fee2005mar01.htm
Also... does the mailing yourself a letter and leaving it sealed hold up in court , for infringement cases.. ?
This is the "poor man's patent" and it is worthless. At best, it might help to establish a date of invention, but it will provide no protections whatsoever, and certainly is not something that can be used to stop someone else from doing something. The only way to establish your rights to an invention are to patent it.
