Old Tamagotchi Availability

[X-Country Pikachu]

So I am searching around on Ebay and Amazon and it seems like the inexpensive new versions of the tamagotchi cousins I'm searching up sometimes pop up on these sites. I'm not exactly sure how long I should wait for one in my price range before buying it. If I'm too hasty about it, I could end up with a better deal later on. If I'm not, I could possibly watch as the last ones are gone. How do the old tamagotchis in general go when it comes to availability online?