The recently released 1001 Spikes is currently $10.01 on the eShop. MSRP is $15 according to the Nintendo.com product page
According to this article on GoNintendo, you're supposed to get a $5 discount if you own any Nicalis title on 3DS eShop (VVVVVV, NightSky, Cave Story, Ikachan or Grinsia)...