Well, the difference is that the "Festive Minigun" was only obtainable with the Naughty Winter Crate (#35) which cannot be opened anymore thus making it more unique compared to the "Festivized Minigun" which can be obtained by getting a "Festivizer" and then applying it on the stock minigun. Meaning there's unlimited stock for the "Festivized Minigun" as long as there's "Festivizer" (which could be used on better things, waaay better things). Now as for the price, I'm not sure I couldn't find a price on the "Festivized Minigun" but a "Festive Minigun" is worth ~1,70€, a "Festivizer" is worth ~2€ buuuuut once you apply the "Festivizer" it loses it's base value and applying it on a stock gun probs make the price drop a lot. So I would guess the "Festive Minigun" is worth more than the "Festivized Minigun".