That's unreasonably expensive. For $68.46 he payed for a day you can have an "el-cheapo" dedicated box or a great VPS for a month. I still don't understand why people trade a bit of system administration and superb performance for a vendor lock and insane prices.
But it's 880 instance-hours per day. So assuming that "el-cheapo" dedicated box has similar performance characteristics to one GAE instance, then you'd need 37 of those boxes. My question is why the heck 31.42 CPU hours turned into 880 frontend instance hours, and whether this is something a lot of other GAE apps are seeing as well.
But measuring process-instance-hour is misleading. In a typical web box, spinning up an extra process takes very little resource since most process memory are shared with the parent process, and most web apps are IO bound, like waiting for network/file/DB, idling taking little CPU. In a server box, many processes can be crammed in (like the shared hosting box). But Google counts those duplicate processes as separate ones and charge the idle time these processes take. That's why you see the outrageous bill.
What's more insane is that Google charges the process-instance-hour like a machine-instance-hour. GAE charges $0.08/hr for process-instance-hour while AWS charges $0.02 to $0.08/hr for the whole machine.