State & Federal auctions, businesses going out of business and unloading equipment, businesses upgrading their racks, and may put them up for sale, e-bay. The list goes on. I found my 3' rack on e-bay about 12 years ago, and got it for a 1/3 of what it normally would cost.
I have been using "Metro" commercial shelving for over 10 years. I use the shelves that are approximately 20" sq. I had glass cut to size, dampened by adhesive backed foam. I even filled the legs with silica sand. Does not cost much, right now I have 7 shelves supporting 200#. Also it is easy to change the config if you wish. It has worked fine for me, who with limited funds, would rather put my my $ elsewhere. The flexibility to easily reconfigure is a huge + for me (it must be as keep repeating myself). I can probably post some pics later later if you wish.