Originally Posted by
WineCountryUA
Surprised there is no buy-up offer in this situation.
Without knowing the OP's base fare and what the cheapest F fare is on the route I'm not all that surprised. Until the day of departure the cash-only upgrade price should be based on the difference in fare between the original purchase and the currently available best price which will confirm into biz, be it M-up, P fare, F fare or something else. If the fare differential is too high they don't always show it.
The discounted offers don't show up until day of departure AFAIK.