Question

How much would a bot that creates twitter accounts and post/favorites/follows/retweets a user cost? is it possible now adays?

I'm sure you can find someone on this forum that will code you a bot like this but it's not gonna be free. As far as post/favorites/follows/retweets other users you can't go wrong with FollowLiker, although I haven't purchased the Twitter version the Instagram one is working just fine for me. To answer if it's possible, yes.