That's kind of vague tbh. Unless you're buying a mass produced product or common commodity there is no 'normal' price. It's like asking what the normal cost of a car is. There's a lot of variation in the cost depending on who made it, how it's made and where it's sold. Additionally, "something decent and nice but not expensive" is dependent on perspective. Maybe a $100 set is decent, but compared to a $300 set it's not exorbitantly expensive.
I'm sure if you went to a department store you could find something not too expensive. It would be functional, maybe mass produced but not much different than if you ordered one from Amazon probably. If you want something a bit more personalized, then you'll have to go to a specialty store and then you'll probably have a range of equipment and prices depending on the craftsmanship.
I mean you could buy one on Amazon for $40, but I assume if you want to buy it in Japan then you want something more unique or hand crafted?
yeah a whisk is definitely needed unless you do cold brew which you can pour into a bottle and shake.
the key is usually to get a set which includes a bowl, whisk, spoon, and hopefully a whisk holder
You will want to do about 1 full scoop and a half scoop of the tea spoon (1.5)
and the key is to pour enough hot water just to cover a little under 1/4 of the bowl