The cheapest EC2 node has one CPU at a reserve pricing as low as $0.003 for a t2.nano instance. The exact math I used is:
(6500 * 365 * 24) * 0.003 = $170,820
I realize that a nano instances don't really have much CPU power available (they're intended to be used for bursty tasks), but Google didn't define what a "CPU hour" was, so neither did I.
Like you said, t2's aren't meant for sustained CPU use. You only get 30 minutes of full CPU use after launch, and they further limit how many t2's you can launch with the full initial CPU credit (100 per day) - so you can't just keep launching new hosts to reset the CPU balance and run out the balance for 30 minutes then relaunch. After you use up the initial credit balance, they throttle the CPU to 5% and each hour they give you another 3 credits (which will let you run at 100% cpu for 3 minutes). They've been very careful with pricing and launch limits to prevent them from being used as a cheap CPU compute farm.
Maybe Google didn't define what a "CPU hour" was, but they surely didn't mean "5% of a typical server CPU".
To get the $.003 pricing, you need to purchase a 3-year reserved instance for $69, so assuming you want to get the job done in a year, you need to purchase 6500 instances for $448,500, if you could use the full CPU. But you can't, so you'd really need almost 20 times that number.
t2's are great if you have a low CPU use case, but once your application exceeds the CPU credit balance, performance gets terrible very quickly (even getting an SSH session open can take 30 seconds on a throttled t2.nano instance), so you need good monitoring and the ability to re-launch instances if you're going to use them for anything significant.