If they want extra it should cost extra on an individual basis I would think.
Not everyone wants these extra things so why penalize them? So in other words this doesnt make any sense. However if you want to up your prices just because the demand is there and your busy then just say that.
No reason to tip toe or make excuses. Honest and straight forward is always best policy.
Something that read more like "Due to demand beyond our original plans, our promo pricing unfortunetly has ended" This is still a great deal for blah blah blah. Or you could add this price point as an "option 2" for folks wanting that full meal deal.