read the 1st line again near the end of my rohan days I used to charge $30 a month mainly for scrolls which u know im famous for.
Theres more **** I just cant remember or its too niche. Since you lurk the forums you will get an idea of whats gonna happen and when and you just gotta prep for them. One of my prime examples would be twins. (inter dungeon farming, I made around 60-80k rps off of that back when it came out with intel from my korean frnds)
A more recent example would be A crystals.... when upg 2.0 was announced the 1st thing I did was make a full party of chars (3 temps+def+priest+pred) and farm silva protectors for A crystals. I made about 6-7k ecash off of that which was ok (price dropped pretty fast damn undercutters!)
so best advice is keep an eye on whats gonna be in demand and stock on it :P