This is permissible. Rent is only due at the end of every month. Any price differential for later payment would be, in effect, charging the purchaser for temporary use of the seller's fund - Ribis . According to the above reasoning, it may follow that in today's business environment, terms of trade would no longer pose halachic problems. Few if any transactions are immediately payable.
Credit is an accepted part of the business milieu.
Ribis only exists if an obligation to pay is delayed in exchange for some consideration to the creditor. Here no financial obligation exists till the end of the month. Yet, despite all possible justifications for the practice, Rav Breish advocates use of the traditional Heter Iska wherever possible.