Ditto on finding good deals on equipment. The problem is if you don't live in a big city your chances of finding good USED gear at reasonable prices are slim. The internet is rife with pieces of used equipment that are either scams or you are basically buying a pig in a poke. The "buyer beware" and "if it seems to good to be true it probably is" should be your watch words if you are buying anything off the internet.
I have been very lucky in buying used equipment but most of it has come from fellow mastering engineers or from people I knew and trusted.
I have been scammed a couple of times but not for any big ticket items.
The other place one can save money is by building or helping to build your own mastering room and acoustics if you are at all handy with tools. I helped build my mastering studio with my good friend who is a master carpenter. He did all the construction and I was his go-fore and holder of drywall while he screwed it into place. I also helped him with the acoustic panels and other acoustical treatments. I paid him for his time but since he was a good friend he did it at a reduced rate. If I would have had to pay full rate my studio would have cost me three times what it did.
Hope this helps!