You'll have to RuneScape gold pay for your own expenses, such as purchasing a wizzy bomb, or using the al-kharid gate. Dragon Slayer - Able kill an lvl83 dragon without range, 15k (with an mage at lvl 33 and an air rune) however, not able to kill any lesser demons.
Since you're not a paying player, I'll tell you the best methods to get dragonhide body parts that are green. The grand exchange can provide the nats as well with the bodies. The most you will get from that, is making 20gps per alch however the maximum you could lose would be 100gps for each alch. It would take 200 hours to finish 55-99 high alching. It would cost between +3.9m and -19.8m. It would yield an alch of 198k.
It is necessary to first attain 55 magic. Spend 200-300k on fire strike or earth, then spend the rest on lessers. You could use fire strike or firebolt on monsters to reach them. It is impossible to estimate how much it would cost, as monster drops can be random.
You could also use curse to increase your level. for 99 that would cost you 17.9. The cost would be to purchase 449k bodies, and 898k water (don't make use of earths since you will need 3 waters instead of 2; it'll be more affordable that method). Be sure to have plenty of heavy metal armor and any other items that give the negative (-) or magic bonus. It is important that you don't allow your curse to affect monsters. Even if you fail, you will get the same exp.
Since the increasing price of pure Essance at The Grand Exchange (and when i became an active member at the same moment) I have made 300k+ per day in just 3-4 hours. (Pure Essance costs 115ea +!!)). but at my level, there arent many things i know of that cosrt heaps, i already own a full rune as well as a full mystic (red/black style) obsidian cape! granite maul, and want to buy something cool looking that isn't rune (g) or (t) (i am buying some (g)/(t) items) or buy RS gold maybe i'll spend it on some other person.