Spud of Doom

Figuring out the total cost for these cruises is pretty complex, and there's a lot of margin for error when you try to estimate on-board costs (especially excursions).

If you were to go fully barebones and look for the cheapest world cruise base price, a lot of the ones from UK/Europe are cheapest. In (roughly) ascending order of price:

• Costa, C&MV, MSC, and P&O UK look like they could even be done for below $20k per person, but only cover the basics of lodging and meals.
• Fred. Olsen, HAL, Cunard and Princess are a small step up in cost, but their itineraries (especially HAL) look better to me.
• Crystal and Oceania (starting more like 45-55k) seem like a real tier above, with more ports of call, more inclusions (laundry options, gratuities, many drinks, some excursions)
• Viking, Seabourn, Silversea and Regent are the top end, costing even more but typically throwing in extras like flights pre- and post-cruise, WiFi, and lots of excursions. Viking ends up cheaper per day than the others with the extra-long itineraries they are currently advertising. Silversea is even pitching one of their 2021 world cruises as an "Expedition world cruise", which visits both Antarctica and Svalbard in the same itinerary.

Honestly, I found it easiest to just get a bus or train to Circular Quay and walk the last 100-200m from there. As long as you're not going during the commuter peak.