Good morning Alex:
There are very few free resources and the ones that are the best have some associated price tag with them. The requirement that you must have 35-ish PM-specific training from a PMI-approved provider has also raised the barrier to entry by a little. From a personal perspective, you will find the best resources right here with OSI. The PM-Prepcast was top-notch in during my preparation and the Exam Simulator is an absolute must. There is a host of reference material that you will also need access to, but you may be able to get some of that from a library.
PMI may offer discounts on membership (not required to take the exam) but there will be no discounts available for application processing or exam fees. PMI membership comes with a copy of the PMBOK guide, which is an invaluable resource.
You will find that professional-level certification is not cheap and certification maintenance also has a cost. You may want to count that cost into your budget as well.
Best of luck.