yeah it is absolutely ridiculous what they charge if you arent a resident.

if you can do without internet while roaming about, you might want to see if one of those small wireless routers would cost less than a softbank rental and subsequent data fees. at the very least you can plug in at a hotel or a friend's apt and get internet then.
far from ideal, but unless you can borrow a SIM on contract, youre going to have to pay too much for 3G data. -_-;