You can go for BotRK if you need it pretty much like any other item that isn't part of the Core Set.
As for Prowler's clas, I'm not a fan, because with this build it feels like a one-trick item. This build in its core is bruiser focused and thus requires items that fit that role - Hp, damage and sustain. These allow for more durability and survivability in fights or in the jungle (you are clearing the dragon and you get jumped, you better have hp and sustain to survive that and/or fight back).