There are blue posts explaining all the processes step by step and lots of people are still missing the point.
The 35$ cloning service is required if you want to clone the character to be available in both Classic and TBC. You do not need to pay anything to play your character in tbc classic.
I don't even care too much about classic expansions but seeing so many people post fake bullshit about this is triggering me hard.
Just read the instruction https://worldofwarcraft.com/en-us/ne...in-wow-classic and stop making clowns out of yourselves.