Mind you, that there are a lot of things that you can do to reduced the price, but I will mention it later.
Now, for the question that about IS IT SAFE TO TRAVEL ALONE TO JAPAN?
I would say, yes.
I've travel to Japan alone in 2013 and I have no problem.
But of course that will be back to you, because even though the crime rate in Japan is low, that doesn't mean you should let down your guard.
Don't travel alone at night, especially in quiet street.
And please avoid making trouble with the local....
Now, for Japan travel cost!
Going from Osaka - Kyoto - Tokyo - Sendai
.... It was 10, but I cut 2 days because it's for plane travel to and from Japan.
IDR 5,800,000 (Singapore Airlines - Promo Economy PP, JKT - Kansai Airport - Osaka and Narita Tokyo - JKT)
IDR 3,202,100 (JR Rail Pass for 7 Days)
IDR 6,400,000 (Accommodation)
IDR 1,320,000 (Food for 8 Days)
IDR 330,000 (Entry Visa)
IDR 550,000 (IC Card)
Total : IDR 17, 602,100, or round it up IDR 18,000,000
The detailed is as follow :
1. I take the Singapore Airlines promo. That goes with 30 kg baggage check, dinner and also breakfast. It was a night flight, so I arrived in Osaka in the morning. When I got back, it was a "morning" flight (11,45, so I check in about 9,00 or around that) from Narita Airport. I got snack and lunch on the return flight. My guess is the flight will be about IDR 5,500,000 - IDR 6,500,000.
2. Some of you might think that JR Rail Pass is not necessary. It is necessary for me since I used it to travel with Shinkansen. JR Rail Pass is worth it, if you are using Shinkansen AT LEAST 3x to cover up the cost. Remember that you can check the Shinkansen price using hyperdia. com. As for IC Card, take notice that the IC Card SUICA can be used in Kyoto, Osaka and Sendai. However, ICOCA can only be used in Osaka and Kyoto. You can only buy SUICA in Tokyo (at least that's what the Information Attendant told me when I arrived in Osaka).
3. For accommodation, I was staying in the hotel with budget IDR 800.000 / night. You can cut this cost in half by staying in Hostel or using AirBnB. If you have friend where you can spend a night during your stay, that's even better.
4. For WiFi, even though my cousin rent it, I hardly use it. Since I plan everything the night before using the hotel's WiFi and asking the Tourist Information Center. You can rent the WiFi once you arrived in the airport, there's a lot of choice to pick.
5. For food, my limit is 1500 Yen / day. Usually I ate more in dinner instead of lunch or breakfast. For breakfast, usually I limited myself for 350 Yen (2 onigiri) and I saved 1 onigiri for lunch. Inari Soba or Kitsune Soba can cost about 350 Yen. Yoshinoya and Sukiya cost around the same price too. So spend wisely. You can also spend less in a day and spend more for tomorrow.
6. For Visa, if you have e-passport, you don't have to pay for entry Visa. But you have to take care of it first at Japanese Embassy. Since I do not have e-passport, I can't really help you in this... ^^a
I hope that is enough information for you guys! ^-^