It isn’t.
The real cost of the FairTax to a taxpayer is the effective tx rate which is frequently about half your present effective tax rate. Your effective tax presently is nothing like the 35% marginal tax bracket you’re in (or whatever marginal bracket you might be in). It is the amount after filing your annual tax paperwork and receiving your refund.
THAT is your present effective rate just as your effective FairTax rate is much lower and is something you can calculate using one of the FairTax rate calculators which have had links on these threads. Many things are not taxed under the FairTax since they are not consumption.
Pretending otherwise is just that - pretense.
My effective tax on my doctor visit today is 0%. Under the FairTax, 30%.