James,
If by "low-cost or discounted" you mean "free" there are not too many resources out there that fit that bill. I found the material that OSP offers, (PrepCast course and the Exam Simulator) to be invaluable in my preparation.
All in all, I probably spent less than $1200 to prepare for the exam - which includes PMI membership (not required), exam and application fee, a hard copy of the PMBOK guide, the PrepCast Course and Exam Simulator (here) and few good prep books (Head First comes to mind) and a couple of less-than-worthless purchases that was supposed to help but were just badly written and presented.
If you want the goods, you have to pay the tariff.