I say don't buy anything, go put your money in the miscellania kingdom and have them get you coal and fish. Put 10 workers on coal, the rest on raw fish.
Also, I'm sharing the account with him right now. I'm not touching the cash unless he wants me to, all I'm doing is slayer and soon avanies. We'll worry about PKing once we actually SEE the update.
Merchanting barrows armour made me like 120m. I don't know if it still works anymore though. If the stats on the account are good, why not buy some supplies for GWD? or Fire Cape? :x