I wouldn't recommend powermining. Sure, it's the fastest XP, but as a free player, I think you're going to be a little disappointed with your ability to actually get rune ores. 85 mining is worth having, to be sure, but I think you're much better off if you have something to show for it once you get it. I would recommend using mining to get some smithing and magic XP along the way by superheating mith. Since you need to mine 24k coal, that's 6k mith bars. If you don't have a lot of money for mith ores and nats now, just start out doing 100 or 200 at a time, and the whole thing will eventually fund itself. Since your smithing is pretty low, you'd probably be better off selling the bars you make, for a profit of 300-400 per bar. You would also score 180k smithing xp, and 318k mage xp along the way. And make around 2m. See, you have 80 mining but almost no cash on hand - that's what happens when you powermine. You're much better off mining things that you're actually going to put to use. Sure, it's slower xp, but it also gives you a lot more freedom to take breaks along the way to work on other skills that might also require some money to get going.