If you just want something very economical to propel you around the neighborhood you can pick up a brand new one for just under 10,000 yen in many places. You can pick up a folder for somewhere between that amount and double.
I have no experience of bicycles on trains or of staying in a hostel. I'm pretty sure you can carry a folding bicycle on the trains, but you may be required to bag it. I think some bicycle messengers in Tokyo sometimes make use of the subway system for portions of their trips with their bikes bagged.
How much distance you plan on covering? Before I had my car in Japan I used to ride some long distances on my "Mama Chari". They aren't the fastest bikes in the world but they are super comfortable and the basket in the front is nice for carrying stuff. Later I upgraded to a Mtn. Bike with street slicks for my daily commuting in the city.
Make sure you get your bike legally whatever you do. They are anal about that in Japan.
You don't need a license, but you do need to make sure you purchased it or can otherwise show proof of having come into possession of it legally. Normally when one purchases a new bike one pays an additional 500 yen or so to have it registered in an anti-theft (insert uproarious laughter here) database. When you do that a sticker with a serial number will be affixed to the bike and a record of your ownership of the bike will exist. If you get a used bike from a friend, have something to indicate that the bike was given or sold to you. Make a copy of it and carry it around in your wallet. Many foreigners have had the aggravation of "inheriting" a used bike from a fellow foreigner who returned home, leaving them behind with a bike registered in another person's name and no proof of transfer. A very good way to spend a very unpleasant and unproductive day at the police station.
If you find a bike that you think has been abandoned or stolen, you can report it to the cops, who will come and get it. They will keep it in storage for six months, after which time it becomes yours if it goes unclaimed by the registered owner. (Yes, I've gotten one like that).
And, actually, one more good source for advice here is our good-ole, unswerving cyclist himself, ADMIN 1 !! I'll shoot off a quick PM to him, so that maybe he can get back here and give some good input....he's done a lot of long-hauls, just like Mike Cash...but on a two-wheeler rather than in an (oh no...I forgot Mike...how many wheeler? not 18 here, right?)
Thanks Mike...I'll try to remember it this time. Yes, you are very welcome Admin 1 !! I'd like to be out on a good set of MB wheels just at this very moment, rather than in the office here.
I wish you all the best hutchi san !! Let us know when you come. Try to swing by Nagano prefecture and you can stay a night or two here, and use the place as a kind of basecamp to check out the Japan Alps--maybe even take a trek up to Kamikochi !! (it'd be a tough ride, but absolutely unforgettable !!! A once in a lifetime, and lifetime maker of a ride !!! MM
thanks all you have been a great help. im looking to come over at the end of the autummn next year and staying for a couple of months, but as im still a uni student i have need to plan and start to save now, as we all know uni students are always poor bloody tution fees. thanks again
I would highly suggest a bike if you can buy one, I got mine for about 6000 yen used, and it worked great. I couldn't tell the difference between it and a new one. Note though that bicycles people use in japan mainly are the old school ones with the baskets on the front, not mountain bikes like everyones uses in the USA. You can get the old school basket ones with gears too though (most of them only have a single gear though), mine had 3 gears, which is all I needed.
For your case though, I would suggest a fold-up bike if you want to take it on the train, as others have suggested. I saw some being sold used at a bike store for around 9000 yen. You can't take a standard bike that doesn't fold on the trains.
I lost my bicycle registration the week after I got my bike, big mistake, but I was never asked for my registration by the keisatsu the whole year I was there. Lucky! =)