Best way to find an accomodation as a long term tourist

Hi,

I'm planning to go to Miyazaki on Kyushu island next month. I will come as a tourist and I want to stay for probably 5 months for yoga and surfing.

What recommendations do you have for finding a cheap small 1-room-apartment or a flat share with private room?

What I found via Airbnb or booking.com is kind of pricy (930€+) per month.

I found one apartment via gaijinpot.com which would be good, I'm waiting for the response of the agency.

I was looking for social apartments / share houses but I only found one in Miyazaki via the website origami-book.com. The deal would be extremely good, but it's totally occupied and doesn't even accept inquieries currently.

If I can't find anything I was thinking about moving into a hostel first and asking local surfers if they know anything or asking home owners with a garden if I could camp in their garden for a fee

Thank you!

I think your last option is a good idea. Once you're there and start making friends somebody is likely to have leads on better housing or even be willing to take on a roommate.
If you're willing to camp there may be actual campgrounds in the area. Did you check?
The nice thing about Japan is all the public baths so even if you are at a rustic campground you can still go to an onsen or public bath regularly.