Re: Not so great
The per-request fees aren't the only charges you'll incur. Both services also charge you for data transferred out of the data centre, and those prices are likely to dwarf the request charges.
If each of your requests result in 1kB of data out (in most real workloads, it will likely be more), 100,000 requests is 100GB of data. At the $0.12/GB pricing of both services, you'd be looking at $12 in charges. So the total cost for those requests is a lot closer than it might first appear. As your requests get larger, the per-request fees become even less relevant.