It's the cheapest but it isn't guaranteed she will be there. OP is asking where kushina will be guaranteed to be and where it is the cheapest to get her. That's a very hard question since majority of the ninjas aren't guaranteed to be a one single event. Without context and listening to your advice, OP would wait until naruto ramen to show up and wait to see if kushina would show up - if not, would complain kushina not showing up....

It's natural to seek help but it's your job after receiving help to learn for yourself. If you're going to ask for help everytime you don't understand one thing, you aren't going to enjoy things as much as compared to you feeling accomplished on figuring out an issue yourself.