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A side-by-side at three traffic tiers, with the hidden costs that the App Engine calculator does not surface.
When you set up server-side GTM yourself, Google's recommended path is App Engine. The pricing calculator gives you a number that looks low. The actual cost, after the parts that the calculator does not include, is usually two to three times higher. This compares the realistic cost against SprTags at three traffic levels.
| Cost item | App Engine | SprTags |
|---|---|---|
| Compute | $40-50/mo (3 instances minimum) | included |
| Egress | $5-10/mo | included |
| Logging | $3-8/mo | included |
| Plan | -- | $5/mo |
| Total | $48-68/mo | $5/mo |
At low volume, App Engine is dominated by the minimum-instance fee. SprTags wins by an order of magnitude.
| Cost item | App Engine | SprTags |
|---|---|---|
| Compute | $80-120/mo | included |
| Egress | $30-50/mo | included |
| Logging | $15-30/mo | included |
| Plan | -- | $20/mo |
| Total | $125-200/mo | $20/mo |
At this volume, App Engine costs scale roughly linearly with traffic. Expect $800-1500/mo for compute and egress combined, plus another $100-200 for logging if you keep verbose logs. SprTags Agency tier is $150/mo for up to 15M events, with overage at $1 per 50k events.
Engineering time to maintain App Engine: certificate renewals (rarely automated cleanly), workspace publishes, container updates when Google ships breaking changes, debugging when traffic spikes. Across our customer base, teams running their own sGTM spend 2-5 engineer-hours per month on it. At standard rates that is $200-1000/mo of cost the calculator does not show.
If those hours are genuinely free (you have an engineer who enjoys this work and has spare time), self-hosting is fine. For most teams, paying for a managed service to keep it boring is the cheaper option once you account for time. The SprTags pricing page has the current numbers.