Harris is running a greens business providing organic spinach, kale and lettuce to specialty stores in the area. On October $1,$ he has $25$ units in stock at a cost per unit of $$2\mathrm{.}25.$ On October $7,$ he purchases $25$ more for $$2\mathrm{.}75$ per unit. On October $31,$ he purchases $30$ more for $$2\mathrm{.}85$ per unit. He sells nearly all of them, leaving only $5$ in inventory. What is his COGS on a weighted average cost basis?