What is the most easy and inexpensive way to file for my wife green card?

You didn't mention where your wife is presently located. Is she in the USA? How did she get here? Is she still abroad? I'd also need to know both her and your past martial history, whether she has children, etc.

Significantly more information is needed in order to provide a legal analysis of the most appropriate, swiftest and least expensive way for your wife to become a Lawful Permanent Resident (to get a "Green Card"). This includes, for example, information about your own immigration status (Are you a U.S. citizen? Are you a Permanent Resident? Do you have some other status?); information about your wife (Is she now in the U.S.? How and when did she enter the U.S.? What is her current immigration status? What immigration-related applications ever before may have been filed by or for her?); Etc. There really is no substitute for you and your wife to consult with an immigration attorney who, after learning all of the relevant information, could advise about eligibilities, options and strategies to attain your goals, and who then could offer legal representation in the often complex application process.