Ah, sadly no outbound networking requests on the free tier. In my opinion that is a critical use case for a tool like this.
This could be a non-starter if there's really no way try it for outbound requests without paying $25 / month. Hopefully I'm misunderstanding the pricing page.
Edit: The fine print for the custom plan:
> 3 The Spark plan only allows outbound network requests to Google owned services. On the Blaze plan, Cloud Functions provides a perpetual free tier. The first 2,000,000 invocations, 400,000 GB-sec, 200,000 CPU-sec, and 5GB of Internet egress traffic is provided for free each month. You are only charged on usage past this free allotment. Pricing is based on total number of invocations, and compute time. Compute time is variable based on the amount of memory and CPU provisioned for a function. For more information, see Cloud Functions Pricing.