Preferably from someone with a reputation to uphold.
Are you sending first (and then hoping something shows up in the mail later)? If so, then this preference makes sense. But it is unclear who goes first.
how much are you willing to pay?
Normally in a sale there is a buyer who pays for a purchase, and a seller who accepts payment for a purchase.
In this instance, it is worded that the seller is offering a C$100 bill. Thus wouldn't you instead ask how much the seller would require you to pay?
[Brain fart, ignore that. The question above it still is valid though.]