Sounds like you have a good understanding of the inventory piece. By showing zero remaining inventory you would be expensing the closing inventory you sold of $6,726 through cost of goods sold.
Regarding the equipment, if you already deducted this when you purchased it (even if it was years ago), you would not be able to expense it again. This would be taking an expense for the same purchase twice, or as I call it, "double dipping".
If the equipment was never deducted, here is what I'm thinking; In your situation the equipment is like an inventory cost, not really a fixed asset. So it is as if your inventory was understated all along. You could either increase beginning inventory by $3,000 which would run the expense through cost of goods sold, or you could increase purchases by $3,000. The more technically correct way would be to increase beginning inventory. In accounting the term is a "misstatement". Your beginning inventory was misstated.
You want to avoid calling it "equipment" because equipment must be depreciated over the life of the asset, and if you missed out on the allowable depreciation you lose the deduction.
Thanks for using this service and I hope I've helped you today.