How can I apply for an I94 document and how much?

You cannot just apply for an I 94. It might be available to those who have relatives in the military. Speak with an attorney. If you need to restore your record, it is a different issue.

One may obtain a copy of his/her most recent I-94, free of charge through the process described here: http://www.cbp.gov/newsroom/spotlights/2014-04-30-000000/arrivaldeparture-history-now-available-i-94-webpage If that is not what you seek, and instead you are asking about how you may obtain immigration-related benefits and about how much the process will cost, then be aware that there is no single answer to this, and instead you should work with an immigration attorney who, after learning all of the relevant information about you and your circumstances, could advise you about immigration eligibilities, options and strategies and could advise you about the costs associated with each.