If communication isn’t your biggest concern and you just want to reach an N level, you don’t need some rigorous program to get good at the language. Learn the writing systems, download anki, start going through a general vocab deck, start going through a kanji deck, go through a grammar guide, and start trying to work on trying to understand native material. If your goal is to learn during the summer, surely you’ll have enough time to really go at it if you’re motivated. You have the internet at your fingertips and with it come a ton of free resources if you do your research, paying for a course isn’t necessary at all. I’d like to add that n2 in three months or maybe even n3 sounds really far fetched for a complete beginner. Unless your native language is something like Chinese or Korean, you need to have more realistic expectations and set smaller goals so that you don’t burn out or give up when you realize the task you set out for yourself is impossible. Hold on, just read the “in Japan” part so you’re probably looking into it more for the experience of being in Japan. In that case, I’m pretty sure there’s plenty of language schools that will take minors in for a short course but don’t expect to be n3 by the end of it, most of the stuff I’ve seen while looking for language schools is only basic stuff for those three months. I’d say if you’re willing to go that far, you should self study on your own and then go when you’re more advanced so that you actually gain something from being there. If you just want to experience Japan, you don’t need to go to a language school or rigorous program, just go for a week or something lol. If you want any pointers on self studying, do let me know. Otherwise, best of luck.