@ACtaxpayer
Simple answer: enter all your costs (one lump sum) as inventory purchases. This would include both 2018 and 2019 expenditures*. When you show 0 beginning and 0 ending inventory, that will place you entire cost on lines 42 and 4, of Schedule C, as Cost of Goods Sold (COGS). Keep your own separate detailed records of the costs.
*It would be more correct to show your 2018 expenditures as Beginning inventory and enter only your 2019 expenditures as "Purchases". But you'll get the same result, either way.
For the future ("I'm arguably a "dealer" of sorts already plus I plan to do more flips"), you may (should) deduct "carrying costs" (insurance, utilities, real estate taxes, loan interest, mileage), directly in part II of Schedule C, each year.
