For you personally I would probably suggest runecrafting either cosmic or fire runes. For cosmic runes, you should get a few more Agility levels so you can use the shortcuts which require 66 to get through. You can boost 5 levels with a summer pie if you don't want to train all the way up. For fire runes, you can just use ring of duelling and your favorite banking method for trips. Fire runes have increased substantially in price due to Invention so this is much better than it used to be. You'll get ~2.3 fire runes/ess. If you have completed the Lumbridge tasks bring along the explorer ring for more free runes.
While you're doing that you can also take advantage of your Farming level and do herb runs. If you have them, take advantage of magic secutaurs, farming juju potions, and the Greenfingers aura. It's not a phenomenal amount of cash but it adds up: http://runescape.wik...r:Farming/Herbs .
Dungeoneering might also be good to train up as it has lots of good rewards, for example a scroll of farming for a chance at seeds back when harvesting crops, and many other things.
But like you mentioned a lot of the good methods require higher levels, which tend to require money to increase at any decent efficiency. You will get there though .