Want to know something about capes/2 letters OG names or snipes ect.. ? Ask me. :p

Nah, I don't know

how to get a cape, and why some are expensive and some aren't .

Snipping requires a program/script how do you obtain tids?

Sniping a username can be made trought programs, but honestly I use online snipers (chearful ninja but ther is other) like, you pay for a token (5$) and It will snipe a username for you, you'll need to put an account without security question before. For the TID, basicly you got it when you bought your account, but you can ask mojang on their contact page and ask it back if you loose it (They will ask you for a few questions you should know)
Depends what capes you mean, like optifine capes are only see-able with optifine mod and are not rare (they cost only 10$) and the others, call "Minecon capes" (Or all other official minecraft capes listed here: https://fr.namemc.com/capes) are most expensive because they are official and see-able without mods, they are expensive because not everybody can have them, you should go to the Minecon or help Mojang to get one, that's why they are rare, and so expensives.



*Hope I helped, have a good day*