Health care here in the US is certainly the wild card. My guesstimate expense for insurance after RE is $600/month. Theres a good chance it would be even higher, since that is todays rate. Tack on the out of pocket aspect and one has to figure something like 10K / year just for healthcare.
The only thing related to expected cost in this area that gives me the slightest hope is the logical belief that costs simply cannot climb indefinitely because no pne will be able to pay. Business cant be profitable if no one can afford their product.
So taking that expense into consideration, im basically using my current spending plus a few thousand more per year for travel, hobbies, etc as my RE spend, and using the ol' 24x on it to get my number.
And im lucky enough to have a small pension headed my way at 60, which should knock off maybe 1% on my withdrawal rate.
I think as one poster above has mentioned, that if one is still quite young when RE, you might have more realistic optios to return to the work force should the caca hit the fan. If one is older, say in ones 50's, i thnk those options will be somewhat curtailed. Earning more may not be a viable option, so plan accordingly.