Also days of the week are a big factor in how much items cost. On Fridays prices usually start to rise quickly, more people playing so more people buying items. Prices usually peak at around Saturday, midnight, GMT on Cerberus, get a little lower on sunday, quite a rapid fall on monday and normall prices from Tuesday till Late Firday. This is generally the case with popular items.

Less popular items are generally the opposite way around. More of these items are being farmed/crafted because more people come online, not enough people buy the items so they get undercut and thus the price lowers.

I generally make money through skill up PTs (weird :o)

Coffer Keys = 10k each usually.
Beastman Seals = BCNM which can get around 1million per person on a good run.
Items dropped off mobs = Depends... I usually get around 5-10k per skill up run.
XP PTs = 5k - 20k these days if i get lucky with drops. (Xp'ing off Tigers, Cockatrices and Ladons (Wyverns) these days)

Not huge money usually and only really accesable at around lv70 but... I haven't had to farm in ages. Think "Squeeze every penny!" from the Simpsons! *Penny goes through skin and starts traveling up his arm* Argh! :X