Coinbase is the most trusted crypto exchange in the United States, their setup is easy and they also accept debit for instant purchases so you don't have to wait for your ACH bank transaction to settle which normally takes 3 business days.
Step 1: On Coinbase, buying USDC has no fees
Step 2: Go to the Stackr coin store and make your coin purchase
Step 3: Select to buy package with USD Coin(USDC)
Step 4: You will then be prompted to select a network, select POLYGON
Step 5: On your Coinbase, select send USDC via POLYGON(purple logo)
Step 6: Send your USDC via Polygon and enjoy NO FEES!