For the OP:
This outfit
https://www.shopjfi.com/ will cut threaded rod to whatever dimension you wish. You can call-in your order and pick up when convenient. They will also have the washers, nuts & most anything else in the form of metal you might want to assemble a DIY rack. I took mine to a local machine-shop and had one end drilled & tapped for spikes.
These folks will have about any wood you want.
https://www.willardbrothers.net/
And, most any granite counter-top place will have sink cut-outs that they have to pay to get rid of for sale at cheap prices. Think I paid a total of <$100 for the 9 granite shelves I have for my rack. They will generally cut-to-size for little $$ as they don't want the expense of getting rid of the small pieces.
Pretty sure I purchased spikes at Parts Express:
https://www.parts-express.com/