Great question… to establish the going rate for the next block go to mempool.space you will see suggestions for low, mid and high priorities. The lowest it will ever be is 1 Sat/Vb.

To your second question, the transaction will eventually always go through at the lowest rate, it really is down to how long you are willing to wait. In the last bull market it would not have been uncommon for you to wait days, weeks for the transaction to go through at the lowest priority.