I wasn't actually aware that there was so much demand for the Halloween rats currently

But I feel that kind of goes with any new event pet that's moderately rare, people start going crazy for it. I remember in July the Gold Macaw was insanely priced, I saw users offering tons of C$ and old rares for it, and it just turned out to be an Uncommon. Same thing with the Carnival event; if you missed the lion carousel pets they were extremely difficult to litter swap for.
I personally really love rats and this litter is definitely near the top of my favourites. I will say I enjoy the general unpopularity of them - even though it makes me a bit sad sometimes they're a lot easier to trade for as a result. Hopefully everyone who's struggling to get the rats they need will manage to do so in the next few days, when the hype goes down, or at worst after the event ends and the rarities come out. ^^