If the card you're casting as the cascade ability resolves is one of those cards, you may choose to cast it as either of those spells that has a lower mana value than the spell with cascade
I love this pair so much, and they are cheap on the secondary market as well, too, by the by
(2025-06-06) You cast the instant or sorcery while Seifer Almasy's last ability is resolving and still on the stack
Id still be willing to give them a shot, mostly because I love Martyr of SandsMartyr of Sands
Its classic and good in a multitude of formats, and I think its perfectly balanced
If the activated ability's cost contains a choice, such as a creature to sacrifice or a number of counters to remove, the copy created by Vantress Visions uses that same information