Of course "overly high airfare" is a loaded term. What's overly high to you?
I'm a big fan of round-the-world tickets issued by member airlines of the two big alliances (Oneworld and Star Alliance) which allow RTW travel including up to 16 flights over a 12-month period. A route like you're describing would be a piece of cake using these products, but there might be some hidden benefits that you could use to leverage the investment even further.
Take
this route as an example. This "Oneworld Explorer" ticket would start in Vancouver BC (see below for why) and go to London, then Rome, then Qatar, then to the Maldives before Sri Lanka. You'd return to North America via Kuala Lumpur and Tokyo.
However, you wouldn't be done. Because the tickets are good for a year, you could stop at home (I've used San Francisco on the map, but it could be LA, Seattle, wherever) for a long "stopover" and use some of the remaining available segments for a second trip. In this case I've shown one that would take you to Costa Rica, but it could just as easily have been New York, or Alaska, or any place else in North or Central America. The Oneworld Explorer allows up to six flights (takeoffs and landings) in North/Central America (including the Caribbean) and four flights in any of the other continents touched, plus the intercontinental flights themselves) so in essence it'd be good for two separate trips - the long round-the-world one, and a shorter all-North/Central America one later.
The reason for starting in Canada is that the base prices of RTW tickets vary hugely depending on where travel begins and ends, not on where you live. For example, the route in the map would include three continents - North America, Europe/Middle East and Asia. The three-continent economy class RTW ticket starting in Canada carries a base price of US$2716. The same ticket starting and ending in the US has a base price of US$3869. You can surely fly from your home one way to Vancouver for under $1153, right?
This route is one of an infinity of possibilities. I haven't included Mauritius because getting there on Oneworld carriers is really hard of late; only British Airways serves MRU from London Gatwick, and with the Oneworld Explorer not only would the price of the base ticket go up by over $1000 to add a fourth continent (Africa) but the routing rules for the ticket would complicate things horribly. The Seychelles are similarly regarded as part of Africa by Oneworld, so the same routing and cost issues would arise there. If the Maldives weren't your cup of tea, you could substitute any number of other islands in Asia in its place - Borneo? Somewhere in Indonesia or Malaysia? Or Hong Kong or...? Many options.
So maybe you could clarify your price sensitivity and also when this trip would take place. Happy planning!