I don't know if Hoso Uni will sponser your student visa, but it is the cheapest certified degree here. I guess it is good for your Nihongo study as well. You can be a student there for up to 10yrs; however you cannot get your full time position with your student visa.
Or start your own business?
http://www.u-air.ac.jp/eng/index.html
Depends upon cases, but a part-time bilingual helpdesk position starts from around 1600JPY/H, I suppose.