To buy all artwork it will cost you 2,390 experience. You will receive some of each Chapters artwork upon completing it for free and the rest you will buy with experience. With that said, you can either beat the game and do some trials in order to get the exp required, or you can grind for it. One of the better grinds is at The Butcher in Chapter 6. After killing it, you restart to checkpoint and
DO NOT pick up the key. Just do this process over and over as the video will show you. Here is a video to help,
As well on this post,
http://www.gamefaqs.com/boards/952493-castlevania-lords-of-s... it was stated that "Chapter 5 Wygol Village: At the 3rd and final ghoul "spawn" point allow them to keep spawning. There is a neutral magic statue nearby which allows for essentially infinite magic use. When the ghouls pop up from their hidey-hole nuke them with "Holy Cross" (or your fav area attack, I think holy cross works best) for an easy 500exp. They keep respawning every 20 seconds or so." Although it is in terrible resolution, here is a video for what that gamer was describing:
Hope this helps! If you have any suggestions let me know.