>>8004142There are a LOT of different versions from the past 20+ years. Consider what you're collecting for; do you want to play the many different versions, or do you want to collect the different shells?
I suggest starting small, go through the lists of different kinds of Tamagotchi and consider which ones are the most interesting to you. The Wiki has a list of every version, and almost every page has a shell design page.
https://tamagotchi.fandom.com/wiki/Category:List_of_all_Tamagotchi_Releaseshttps://tamagotchi.fandom.com/wiki/Category:Shells_listsAlso be sure to check out selling/trading groups. eBay tends to be hit or miss, with stuff either being grossly overpriced, or the seller is putting something out cheap with no idea of its actual value. Vintage P1s and P2s tend to go for fairly cheap, and used m!x and Meets models tend to go for $30-40. You can also buy from JapanYouWant (a site that specializes in Tamagotchi, fairly reliable), or Yahoo Japan Auctions via Buyee.
This price sheet is often passed around in the collection groups:
https://docs.google.com/spreadsheets/d/e/2PACX-1vSzl3kki1KTw_XvmX_qWjZ5CSm1TRjkdXb4IPbTYpru8W5nSX4uMA_arw25n-oEeoltfhJiCXA3TP6K/pubhtml?gid=0&single=true 