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Well, wouldn't be the first time my numbers were wrong! But even using your $6 per gallon price, it doesn't add up to the difference between the two countries.
As there is no such thing as a fATPL in the US (and if truth be known, you only have an ICAO CPL), we cannot compare like with like, but the question was PPL->CPL.
Let me throw out some realistic figures for zero to Commercial Pilot-Multi Engine Land-Instrument in the US, and as I know where you like to rent in the US and the instruction there is the best you will find, lets use their prices (block). Sales tax of 8% included in solo rental, not charged on instruction rental. Instruction at US$38 per hour (again block rate).
VFR Warrior: Solo US$61. Dual US$95.
IFR Warrior: Solo US$71. Dual US$104
Super Cub: Solo US$63 Dual US$96
Twin Dual: US$200
Arrow: Solo US$103 Dual US$134
And lets have fun along the way, lets spend 20 hours getting checked out in a Great Lakes Biplane.
2TIA-2 Dual US$180
Lets also head to the Colorado river, spend a night in the casinos, and get your sea plane rating (5 hours, US$800 out of the door)
So....
PPL in a super cub/VFR Warrior. 40 hours dual, 25 hours solo = $5400.
Hour build in VFR Warrior/Super Cub. 75 hours = $4300
IR in warrior, 40 hours dual, 20 hours solo = US$5600
Great Lakes Checkout. 20 hours, $3600
Sea Plane rating (PP-ASES), 5 hours, US$800
Now have 225 hours.
CP-ASEL in Arrow, 15 hours dual, 15 hours solo US$3500
CP-AMEL with IR. 15 hours Dual: US$3000
Add $1000 for quizzes, and $1000 for books/headsets/gear etc
So, 265 hours later, you are CP-AMEL/IR, PP-ASES and can solo an aerobatics taildragger biplane.
Grand total - around US$28000, so a little bit higher than I first said - but I was assuming CPL in a single. Knock off the CPL in a twin, and you have around $25k.
For the hell of it lets round it up to $30k.
BUT this is actually quite extravagant.
If you joined one of the even cheaper clubs at Montgomery Field San Diego (no sales tax on club rentals there), or did it in 200 hours under part 141, or didn't do the ASES and aerobatics add ons, you could easily get CP-AMEL/IR for under $25k. Also mine are high realistic figures for instruction, most average students could do it in less dual and do extra hour building in a cub for US$62.
Also, under the US system, you can split the cost of rentals by one person being under the hood and the other being safety pilot. You might disagree with the principle, but it's legal, and will take your hour building cost per hour down to the mid $30 range.
Hmm, better add another grand for losses at the blackjack table, that sea rating is more expensive than I thought!
Cheers