All 3 of the Castlevania DS games are currently on sale with Amazon. You can get Dawn of Sorrow, Portrait of Ruin, and Order of Ecclesia for around $20 each brand new. Also the 3DS version of Lords of Shadow - Mirror of Fate is currently less than $20.
Castlevania: Lords of Shadow - The Collection is currently on sale with Amazon. You can get the PS3 or Xbox 360 version for less than $20 brand new. LOS Collection includes both DLC Packs, and an HD version of Mirror of Fate. LOS 1 and 2 are also on sale separately.