One place to look is Ebay - I've seen some good prices on some Gibraltar and Pearl pedals.
eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices double bass drum pedals | eBay
for example, see items: 180649728622, 140530762385
If you are comfortable with Ebay and know how to research the products and sellers, you should be ok as long as you buy a good brand: Gibraltar, Pearl, DW/Pacific, Yahama, etc. Stay away from the aftermarkets and try to get one that is chain drive rather than direct or strap.
In other words, stay away from brands: BadAax, TKO, Vex Pro, etc. Some of them look as if they are constructed ok, but ...