I agree with atronic92, but I'd actually suggest doing Dragon Slayer at 40 defence - the experience will push you up a few levels, then you can get 45 for berserker helms, since you're getting P2P eventually. :P Right now, at your low defence, minotaurs and flesh crawlers are great experience. A load of trout/salmon will last you a very long time... ...and why not train fishing and cooking and fish your own fish right outside? All you have to bring is an axe, tinderbox, fly fishing rod, and feathers. Until you run out of feathers, you can stay there forever! :) The only costs would be buying feathers, but you could always get those on your own, just kill some chickens. A few thousand feathers would get you a few fishing levels, and those few thousand fish would last you many, many strength levels.