Start looking at Craigslist in your area... I've seen many gently used WDH setups being sold for a fraction of what they cost new. I upgraded the two Curt spring bars on mine last year, buying 1 bar from Amazon and 1 bar from Ebay (same make/model/weight rating). Both came from wholesalers who were getting rid of excess inventory, and I paid less than half of what they would've cost new from Curt.
Of course you'd normally want to see used equipment in person, to make sure none of the components are damaged or missing. But given the amount of use that most WDH systems get (not much), even most used WDH's would likely be just as useful as new. In my case, Amazon and Ebay both have money-back guarantees, and I verified with the seller(s) exactly what I was buying... so I felt confident buying sight unseen.