uhh.. really? well when i played like 5 years ago mining coal was one of the best jobs around for any lvl 20-45 then it was yew cutting for 45-60 and then market trading and quest.
When I played it, I found, as a nonmem, mining coal works well. Also, if your smithing level is high enough, you can buy in the grand exchange tons of coal and iron (twice as much coal as iron) and smith it into steel, then sell it. This way, my money went 2000 -> 5000 -> 20000 -> 68000 -> 90000, and it increase more and more each time. Also, wc yews.
Also, my friend is a mem, and he kills spiders and sells their carcasses for 1K ea...fast mem money.
Im a non memb, and I dont play as much but I cut yew logs. It's a little way to make money until I become a member in time to make the real money. If your a member fish swordfish, it's relaxing, you get to talk with the community, and it makes good money!