Another tip: Watch auction sites for the items you need. Instead of buying a new box blade for $800, you might find a really good (but used) one for $200.
I recently won a black powder pistol that the auction company took apart because it was "loaded." So in the photos, it looked like junk. I bought it for $30!! The pistol was loaded, but not capped. Not matching the markings up with the description on the auction listing, I got it appraised. Its not a reproduction, but an original 1846 Colt Walker! The appraiser valued it at $850.
But thats not all, I have found things on these auction sites that I didn't need, but found that they are going really cheap. Knowing what they are and how valuable they could be, I bought them and flipped them for big profits. The one item that came to mind was when a local brewery went out of business, they auctioned off everything. I bought stainless steel tables, sinks, and other kitchen/brewery gadgets. I then flipped them on craigslist for about triple what I paid.
I'm currently in the market for a 3pt sprayer and a QA snow plow. I bid on both of these in a recent auction, but they went for stupid money. So (BONUS TIP) know your limits and do your research! Just because its at auction, does not always mean its a good deal. People get competitive and need to feel like they have won, even if that means over paying for something.