PoA ?

Hello.

I would appreciate if someone could provide
general info about what's precisely the Power
Of Attorney that's filed with a Patent Apllication
(when such obligation does exist). More in
particular:

1. The average costs of a power of attorney in
patent attorney firms (I understand it's about 100$) ?

2. Can I, for example, sign such a document,
provided that I'm obligated to, and file it to the patent office,
however, communicate with the patent office
myself without the attorney actually doing anything
despite the PoA ? (In case, for example, that I am
able to handle all matters myself and am not intrested
in further expenses associated with the attorney's services.)

3. The signing procedure of such a document in the
P.A.'s office.

Thanks a lot.

What is the name of your state? "1. The average costs of a power of attorney in
patent attorney firms (I understand it's about 100$) ? "

Entirely dependent on your geographical location, and what size firm you are working with.

"2. Can I, for example, sign such a document,
provided that I'm obligated to, and file it to the patent office,
however, communicate with the patent office
myself without the attorney actually doing anything
despite the PoA ? (In case, for example, that I am
able to handle all matters myself and am not intrested
in further expenses associated with the attorney's services.) "

No. Once you sign the POA, the PTO will only deal with the attorney. From the Manual of Patent Examining Procedure, Section 403 and 37 CFR 1.33:

"The Office will not engage in double correspondence with an applicant and a registered attorney or agent, or with more than one registered attorney or agent except as deemed necessary by the Commissioner."

http://www.uspto.gov/web/offices/pac/mpep/documents/0400_403.htm#sect403

The exception is, of course, that you, as the applicant, can terminate the power of attorney -- but then the attorney can't talk with the PTO for you. You can't pick and choose which parts you will handle and which parts the attorney will handle. If the attorney is charging to much, perhaps you could find an agent that would do the work cheaper.

"3. The signing procedure of such a document in the
P.A.'s office. "

In general, the rules for signing aPOA, at least as far as the PTO is concerned, can be found here: http://www.uspto.gov/web/offices/pac/mpep/documents/0400_402.htm#sect402

The firm may have there own specific rules and formalities in addition to the basic PTO rules, so you should talk with your attorney.