Difficulty of Bitcoin Testnet will be reset to 1 if no testnet block found in 20 minutes.
Your estimated cost is not correct because difficulty reset.
The difficulty number used is an average from mempool.space which accounts for the difficulty resets.
0.00001550 BTC (0.83 cents USD @ market rate) to just buy one Bitcoin Testnet coin in minutes
LOL that's so cheap, I may even buy some myself. There's no incentive to mine even with a USB miner at difficulty 1, when you can buy a whole coin at such a low rate. The going rate doesn't align with the mining cost and time to solve over 80 blocks with a 0.012 reward.