hard to say
a lot depends on what gear,
what level of quality your interested in,
and what you consider cheap
I often browse Clist for gear, lots of people sell barely used outdoor gear at bargain prices
my current tent is a $200 kelty, that I bought off craigslist for $80 used once
also have a field and stream tent I bought for $20
I sometimes check thrift stores,
have 2 LL bean 20 degree sleeping bags that I bought for $10
amazon takes some searching but they sometimes have open box/returned items at heavy discounts,
things like apparel often gets returned because of sizing,
bought a $50 quickdry tactical shirt for $10 new in packaging
many big name stores often have clearance section to browse,
have bought a few items off dickssporting goods flash sales
basically check various sites and check them often,