Well amazon.co.jp does ship overseas, but they are not responsible for whether or not those second-hand sellers do. So if you want the cheaper one, you'd need a middle-man service which is about 1000yen more (about $10).
Amazon.co.jp usually charges a 2000yen shipping charge (about $20), despite that they can ship it EMS for only 1500yen (about $15). Than you have to consider the 5% tax on all sales made within Japan; not sure if it's higher if you buy it from overseas (like the tax where you live, doesn't seem to be, but I never paid too much attention).
And I don't always like going through a middle man... as it seems expensive enough without one. You don't really get much of a discount that way; if lucky you might save a few bucks buying the second hand one, when there's still a normal brand new one purchasable through the site. Before they rose their prices, it wasn't so bad... it was like only 500yen (about $5) more. So I bought a lot more second hand back than; now it doesn't make much of a difference.
The cheapest I paid for a single back in the day... was something like $12 after shipping and taxes. That was the best deal I ever made; considering the only people who sold the single brand new... wanted $40 before taxes and shipping.
And I only plan to get the Last Summer album; the singles seem pricey.
Besides, the only thing missing off those singles now is the Karaoke's. I know.. the Sora ni Kakeru Hashi ~Unplugged Version~ is very low; you can "normalize" it in either Audacity or Cool Edit if you have it. It's sadly only 128 CBR; the other songs on that single were a bit better I believe, but that's the best version I could find... which is nice, considering I found it at all; I was considering buying the single because I was having no luck finding the song earlier.