Is there a way I can set up a condition on dialogue to check if the player has a certain amount of money in terms of a global times a number?

I'm trying to set up a system where the player can buy something through dialogue. So, they're given choices, buy 1, but five, buy ten, etc. But I only want that to be a choice if they have the right amount of money. The problem being that the cost of this item changes depending on a few things, so it's a global variable. Thus, I need to check if the player has enough gold to buy that amount. If they want to buy 5, I need to only show that dialogue option if they have the current global variable times 5 amount of gold. Is there a way to do this? All I can do is check if they have the global value of gold, times 1. Meaning they could buy any amount of the item no matter what.

Thanks for any input.

Actually, as an alternative, is there some way I can set a buy/sell multiplyer with that perticular merchant? If I can just jam this stuff in a vendor setup, then make him sell it cheaper that would be awesome. I could just use SetGoldValue, but I want the item to retain it's high cost elsewhere, and just be cheaper to buy from him. Hence this whole complex setup.