Tickets prices can vary by country, sometimes to the advantage of the traveller, so here is my contribution.

If I want to start a RTW in another country, can I pay that price rather than my home country?

In order to take advantage of a difference in price between one's home country and some where else, the ticket MUST be issued in the country where you actually begin the RTW itinerary.

In answer to another question, all travel on RTW's are on the piece system. Make sure that is noted on hand-written tickets.