I don't think this data is available anywhere. You could do an estimate, based on the number of players, which you would also have to estimate.
About 650 gp for each piece
about 100 to 200 coins
the grand exchange on runescape
you can get them at the grand exchange for about 1,620 gold coins
Runescape is for nerds
As of today, there are no known places that offer Runescape Gold for free. However Runescape Gold can be purchased cheap at websites, RSgoldfast and Playkiller.
Trading RuneScape accounts is against the RuneScape rules. There is a black market for accounts (and RuneScape gold, which is also against the rules to trade). You can search the Web for keywords such as "Runescape gold" or "Runescape accounts", but note that, being against the RuneScape rules, none of these sites is endorsed by Jagex (the makers of RuneScape), and that many of these sites may well try to scam you.
Do NOT real-world trade, as you will get banned. Earn RuneScape gold yourself.
You can't get infinite gold on runescape.
Selling runescape gold in the real world is illegal. You can "sell" runescape gold in-game for other items on the gran exchange locatedin the north-west corner of Varrock.
60 gold, or with karajama gloves only 30
None. There is no gold in any Australian general circulation coin.