You could do it all in one month, e.g. 5 days Thailand, 10 days Oz (well Sydney / Melbourne) 5 days Fiji, 5 days NYC, and 5 days flying. If you had a few days extra you could try San Francisco en route to NYC. RTWs will come in at about 1,500 – 1,700 each; then add on 100 pd pp, so you could do it for 10,000. I’ve no idea on Fiji, but OZ and NZ are cheaper than Ireland, the US about the same, Thailand is cheaper, so you’d have some cash to spare for the odd splurge. DO you have any friends / relations in th eUS or Oz with whom you could stay? This would cut down on costs as well.