Is it permissible to take out a loan from a Riba-based bank to purchase an essential plot of land, given the unavailability of sufficient funds and the absence of lenders?

If the bank lends you an interest-based loan, you have fallen into usury, which is forbidden by Islamic law and is one of the major sins. You must repent sincerely from it. If you can cancel the contract or reduce the interest rate, you must do so. If you cannot, then you must repent, and you are not sinful for continuing with the contract because you have become compelled to it.