The ego feeding in filia works like the wend. discount, don't confuse it with other cities where the base price is different. Feeding at filia with an allied character gives you a discount on the price, but keeps the base value the same. Saves me money.
Also some people have stated before, not sure if its been proven, that feeding expensive items will carry over to your next feeding and affect the egos appetite.
Personally I don't have the money to feed 40k+ items, so feeding one 40k+ then..not being able to feed another expensive would mess up my next feeding with cheap items, if what people have been stating is correct.
This.
1. If you intend to feed your spirit weapon items under 999 gold, you should shop at Filia.
2. Small gems (less than 5cm) are expensive and slow. Stick to items under 999 gold or large gems/diamonds/loot.
3. Tipping Suits are a good alternative to gems. You can obtain two per rafting trip and they cost 230k from NPCs.
4. Dungeon drops/loot (Kite Shields, Claymores, etc) have low demand and give excellent stat experience.
5. Diamonds are the fastest/most expensive method. NPC items give you the best experience for your gold, while maintaining fair experience gain.