Twitter Account Question

So earlier today on twitter.I got in contact with someone that is selling their twitter acccount.I was wondering how much would a account with only 20k followers be worth?Also the followers are real(I checked)but the account is not that active.But that's fine with me because I plan on re branding and building up the account.Help it gain 20k-50k active followers.So if someone can give me a price range.I would appreciate it.Thanks.