The Derby is fifty shades of downright dangerous. You hopefully already know that. Insurance is very important. Chaps, this really is a one-of-a-kind adventure and you need to pick up the phone and talk to insurers about what you are doing. Many will balk at the word 'race'; you need to explain that this is not a professional event (important distinction from insurer's perspective). Do not put yourself in a position where you could be stuck in Mongolia with a fat medical bill and an even fatter evacuation bill to get you somewhere with the standard of medical facilities you think you deserve.
You need very comprehensive and responsive medical insurance for your treatment/travel for further treatment/repatriation. From an insurer who KNOWS what you are doing.
It's really important that you know how the Derby is classified for insurance purposes. It's not a race, technically speaking, and it's not a sporting event, as it does not fall under any official sporting governing body, like the FEI or AERC. It's not professional, as there is no prize money. It IS an organised ride though. Technically speaking it is more than just 'horse riding in Mongolia'. Please do not hide this fact when speaking to insurers. The Derby would classify as an organised adventure tour.
Some insurers will insure absolutely anything as long as it's not base jumping, deep sea diving, or paragliding, under 'adventure sports'. Including the Derby. Others would exclude it because it is organised fun. It's up to you to check this.
We spent some time talking to Pacific Prime, an international broker, and found policies to cover UK, European, US and Australian citizens. BUPA Global Travel, Cigna, IMG Globe Hopper all had suitable policies for Mongolia. If their evac partner is International SOS, that is a big mark in their favour, as the clinic you would be evacuated to in the event of a pickle is run by ISOS, and the fewer insurers you need to include before purse strings are opened, the better.
Last year one rider insured with US Giant TravelGuard (underwritten by AIG) was more or less left on the side of the road whilst his insurers dithered over who was paying, what an appropriate care path was in Mongolia (they had no idea), and how he came to have a medic on the scene. Please, avoid Travelguard.
Your criteria should be an evac coverage worth at least $30k. This is the approximate cost of a helicopter evac from the furthest reaches of the Derby course back to Ulaanbaatar. In-patient and hospital costs should be generous, in the region of $100k, in case you are hospitalised for a long time in country. For almost all insurers, if you incur outpatient costs, i.e. you are walking wounded and visit the clinic post race, you will have to pay through the nose, open your own claim file, and recoup the costs later. Some insurers will cover outpatient costs but you will pay quite a hefty premium for this.
We don't much care about your door-to-door insurance. Of course you want to be able to claim for your lost camera or if your rain jacket gets eaten by a yak.
Other policies Derby riders have tried and tested include Sports Cover Direct.
These are not the only insurers available and remember that it is your responsibility to ensure that the company you use understands what the Mongol Derby entails and the risks involved. Many insurers may reject your application on the basis that their policies cannot cover you for the risks involved in doing something like this - so you may need to research your options extensively and persistently.