Used Traps

Garage sales if your lucky, out in the farmland areas, maybe craigslist.org

If you live in a rural area, put a 'Wanted' add in the newspaper.

Watch auction notices in the news papers, especially estate sales, they will usually list them and you will normally get them cheap.

some of the smaller flea-markets/swap meets (as opposed to the larger ones that tend to have 'regular' professional vendors week-to-week) that have a good turnover of fresh vendors, sometimes older farms that have been converted to a more 'modern' aesthetic (bed & breakfast or residence) usually don't even use their barns for their original purposes & have treasure troves of good stuff in them, sometimes even free for the hauling! ^_^

Pick up a trapping magazine, they tend to have ads in the back for used traps for sale.