Earlier today an FTer pm'd me asking about cheapest northern hemisphere DONE3 fares and whether southern hemisphere DONE4 fares might be a suitable alternative.

I thought my answer might be of general interest, so I am posting it here.
The list (source: ExpertFlyer) is incomplete, especially with regards to Asia, but I'm fairly sure that nowhere else in Asia beats Japan
Historically, southern Africa has been the cheapest place to start a DONEx - so I've listed the DONE4 fares from there.

DONE3 Base Fares ex Northern Hemisphere
Region/CountryCurrent Cost
USA USD 9,699
Canada CAD 10,199
Rest of Nth Am USD 10,199
Eurozone EUR 6,412
UK GBP 5,471
Norway NOK 52,398
Sweden SEK 58,779
Switzerland CHF 8,520
Denmark DKK 47,737
Japan JPY 656,300
Sth Korea KRW 8,529,300

DONE4 Base Fares ex Southern Africa
Mozambique MZN 357,060
South Africa ZAR 88,410
Namibia NAD 88,410
Mauritius MUR235000

DONE4s ex my part of the world
Australia AUD 11,999
New Zealand NZD 12,699

Putting the numbers through xe.com to get USD figures:

Canada at ~USD 7,650 is the cheapest in Nth America
Norway is the cheapest in Europe at ~USD 6,290
Japan is ~USD 6,560

Southern Africa DONE4 prices are ~USD 6,500
except for Mozambique which is a still attractive USD 5,000
(though not as attractive as they were prior to the price rise on 1 August 2016 - I purchased a DONE5 for ~USD4,000 all-in, and a DONE6 for ~USD4,800 all-in)

So, if someone actually wanted to visit Africa as part of a DONE, then starting in southern Africa is an attractive option, especially Mozambique. But if Africa is not wanted, then the positioning costs might outweigh the lower price ex-Mozambique