The full set of themes and faceplates for the launch of the New 3DS have been revealed along with a commercial.
Themes go from 100 -200 yen and there are third party themes like Monster Hunter, Youkai Watch and Azure Striker Gunvolt
There are two sets that are free though. Simple Clear Colour Set Vol. 1 and Simple Colour Set Vol. 1
http://www.nintendo.co.jp/3ds/theme/list/index.html
Faceplates are plentiful and very colorful. Mostly 1000 to 1500 yen but there are a couple special ones that go for 3000 yen
http://www.nintendo.co.jp/3ds/kisekae/index.html#/top
CM: https://www.youtube.com/watch?v=9MpQSvaduzk
Also Hipster Bowser
3DS Friend Code: 047387541842