You are focusing on the existing savings and ignoring the future of that savings and your ability to save faster under the FairTax.
Look at $100K existing savings, where you are able to add $5K each year under the PIT but would be able to add $10K each year under the FT.
In 5 years, the PIT would leave you with $165K if it earns 10% and then you pay a 25% PIT. The FT would leave you with $225K at that same 10%.
Since FairTax inclusive prices will be 115% of the old prices, you just got a great deal. Instead of being able to buy $165K worth of 'stuff' you'll be able to buy that same stuff for $144K, pay $44K in FairTax, and have another $37K left over to spend on more 'stuff'.
Only under very special conditions -- like Roth IRA's -- where there would be little/zero PIT owed, or you have no time left for the savings to grow, does the FairTax hurt your existing savings.
In 5 years, the PIT would leave you with $165K if it earns 10% and then you pay a 25% PIT. The FT would leave you with $225K at that same 10%.$225 minus 23%(current teaser rate) = $173,000 to spend and if the "basic rate" was 4% you'd pay an additional 30% tax on the remaining 6% earned...Yes there would be a sales tax on some interest earned AND or paid not to mention the new 30% tax on any bank fees.