I just spent some considerable time going through my SDB to scrape together enough items of "estimated value" to get the "I taunt the Pant Devil" avatar (
see avatar.starried.net's guide here). To keep anyone else from repeating my effort, I figured I'd offer some observations.
First, here are some high-value items:
1) One hundred dubloon coins (110,000 NP)
2) Solitaire Champion (109,999 NP)****
3) Genie Orb (106,700 NP)****
4) Scroll of Freezing (92,500 NP)
5) Whoot Necklace (82,500 NP)****
6) Lightning Scroll (67,120 NP)****
7) Greater Defence Scroll (66530 NP)****
Scroll of Dark Nova (65,232 NP)
9) Greater Healing Scroll (65,200 NP)
10) Bone Sceptre (64,250 NP)****
11) Obsidian Dagger (62,110 NP)****
12) Lesser Defence Scroll (55,410 NP)****
13) Golden Geraptiku Talisman (54,200 NP)****
14) Iceray Bracelet (52,679 NP)****
15) Scarab Ring (50,000 NP)****
16) Ghost Paint Brush (40,000 NP)
17) Sand Snowball (40,000 NP)****
**** These items all sell for less than 5000 NP on the SW.
It's also nice to have several Pant Devil Attractors in your inventory, which will hopefully keep your valuables safe (the Pant Devil actually didn't steal a thing from me; I got the avvie in about 20 refreshes).
In general, I found the following items tended to have higher value: battle items (especially rare or "special" items), rarer potions, paint brushes, scrolls, rarer snowballs, (pick-your-own) berries, dubloons, rare/painted petpets, job coupons, rarer scratchcards.
Things that I thought might have high value but didn't include neggery neggs, map pieces, codestones, stamps (although I only had "uncommon" and common stamps), and most food and books. I didn't check out the values of any wearables.
Hopefully this information will make things easier for others who try for this avatar.