My gut instinct is that the right price for verification is something like $1000 as a one-time fee. Lots of people who are active Twitter users will find that fee useful at some point in their life (as a business marketing expense), and Twitter will likely extract a lot more from them by charging $1000 once rather than $8/month.
I think it should just be 3x the cost of their verification process, and something that disappears and needs to be re-done if you edit your name/bio/handle.
