Let's ignore the $0.10/GB-month vs. $0.125/GB-month storage pricing as it is negligible compared to IOP costs.
Standard EBS volumes average 100 IOPS with best effort bursting.
A provisioned EBS volume at 100 IOPS would cost $0.10/IOPS-month * 100 IOPS = $10/month
A standard EBS volume cost would be $0.10/1000000 IOP (an equivalent of $0.26/IOPS-month). The breakeven with the provisioned EBS occurs at 38% utilization (38 IOPS), meaning that provisioned EBS is cheaper above this point.
To match the performance of a 4 volume standard EBS RAID (400 IOPS), you would have a minimum fixed cost of $40/month/GB, vs. the current $0.40/month/4GB + variable IOP pricing.
Provisioned EBS makes sense for scenarios with sustained high IOPS utilization as you get consistent performance with possible lower total costs. For less IO-intensive loads, using a RAID of standard volumes will be more cost-effective.