Hi I never posted before.
I just got back from Japan about 3 weeks ago, I was studying there for a year but was teaching ESL in a conversation school for part time. Most jobs there teaching English you make about $27,000-$30,000 a year maybe a bit more it depends which company you work for. The company I worked for was NOVA, basically the pay rate is around $22/hr when I teach five students which is almost always the case. They also paid for my training and the hotel I stayed at in Tokyo during that time. I use the subway to get to work and they paid for that too at the end of each month. The work is really easy and enjoyable, but I can't see myself doing it for more than two days a week, because it gets super repetitive that you'll just go crazy. You meet lots of interesting people though, but you can't date students. But some companies such as GABBA allow you to date students. These schools are open everyday even during Christmas time and some holidays. Also no use of Japanese in any of the lessons no matter what. I got in trouble for that.
Other than Nova I also had 2 private students and I got paid $20 each per session with them. It doesn't seem like a lot but it adds up and eventually that money is what got me my groceries because I had no help from my parents while I was there. The website where I got my students from is called
http://www.findstudents.net. You basically set up a profile and wait for students to come to you. You can set up your own rate and where to meet etc.
I also helped out at a local elementary school twice and my contact there is the coordinator for all the ALT teachers in Nagoya. ALT might be another option for you I think. If you're interested I could give you her email, she's really nice and polite. I didn't do ALT, but one of my co workers was doing it full time and the conversation school part time. What you do in ALT is you go to a middle school or high school, and you help plan out lessons with a Japanese English teacher. You work 8 hours a day 5 days a week. Nights off and week ends off, except on special school events because you have to help out there too.
I only know about JET program by reading it, and by talking with a couple of instructors. Basically they stick you in whichever part of Japan requires instructors. The one I talked to he got put into the most rural area in Japan for a year. No buildings no convenience stores, just a small village with nothing. No one also spoke any lick of English. This might be good if you are interested in learning Japanese, but without some kind of night life I'd go crazy.
All of these jobs pay at about the same rate, but according to the other teachers I worked with its by doing private lessons where you make ends meet. $30,000/yr in Japan isn't luxurious, its just enough to get by and a few thousand dollars here and there.
If you want some contacts I can share some with you no problem. I was in Nagoya and apparently they need the most teachers there for ALT and those conversation schools. Which city were you planning on going?