Last minute discounts?

I live in Quebec City. I don't have a credit card, but I know for a fact that VIA Rail accept payment trhough a temporary credit card.
Assuming there are last minute discount available for all services within the corridor, where could I go for a small round trip with 100$. I was thinking of Ottawa, or, if not possible, At least Montreal. What would be your suggestion? BTW, the 100$ limit only applies to the actual train trip. Everything else, it'll be handled with real money.

As you probably heard, VIA has a 50% sale until the 19th, with travel to be completed by early Sept. It is for all classes, although Business Class is available at the half-price only to members of the VIA Preference programme. I see no restriction on buying tickets at a station, so cash can be used for payment. From Quebec City, a round trip in Economy (Supersaver seats must be available for booking) costs $75 to Montreal and $110 for Ottawa - plus the sales tax, of course.

Thank you for the reply. However, I did know about the 50% thing. Problem is, I don't have the time nor the money to go buy discount tickets. That's why I was planning to use last minut discount. I'm pretty sure I could get a round trip to Ottawa for even cheaper than 110$ if I time my travels right. Beside, the 50% thing applies on Regular fare (though it requires to have supersaver place available) A round trip from Quebec to Ottawa is something like 120$ on super saver fare, so I'm not saving that much money. (I almost always take the supersave fare) I'm sure getting at least 1 or 2 last minute dscount would be less expencive than that... again, if I time right (By looking at the discount list every day) I just wanted to ask if it WOULD be possible for a round trip under 100$

Still, thanks for the time you took to answer