[naniwaduni]

I think this is one of those places where mass-market financial advice is aimed at people who are bad with money and might not be able to float a month of expenses on credit.

I'm not sure I've ever had a nontrivial expense in the US that simultaneously couldn't be paid on credit and wasn't known for weeks in advance either. I would expect any no-credit charge in excess of about a dinner bill to be announced at least a week in advance, implicitly through an invoicing process at the very least, and I would frankly have reservations about whether any vendor who didn't have a way to handle this was really a legitimate business.

Even if that's not an option, your broker is probably fine with floating you a sum of cash matching your recent MMF sale amount as overdraft or margin at a price of somewhere between "we've already factored it into our fees as a cost of doing business" and <0.05%/day of the loan amount anyway, because overnight loan alchemy is a well-understood problem and the bread and butter of retail banking.