Context: a boy wants to buy a book, but it's out of stock.
nandeshitara hairi shidai otaku e otodoke itashimashou ka 何でしたら入り次第お宅へお届けいたしましょうか [If you want] [I] will deliver [it] to [your] house [as soon as] [it] enters [stock].
shidai 次第 Depending on. In this case, when he delivers the book depends on when it enters stock. As soon as.
sou shite kureru? そうしてくれる？ [You] will do so for [me]?
daikin wa {{sono ba de harau} you ni} shitoku kara 代金はその場で払うようにしとくから As for the payment, [I] will make [it] {so [that] {[it] is paid there}}.
i.e. the payment will be ready at his home for when it arrives.
