There are a few alternative GraphQL gateways (free) nowadays, check the audit I did to measure how compatible they are with Apollo Federation spec: https://the-guild.dev/graphql/hive/federation-gateway-audit

I would say it's hard to build your own gateway, because of the complexity of the Apollo Federation spec and there are literally 0 libraries that will help you build one. When I say it's complex, I mean it, just look at the tests I created for the audit (it's open source).

You could potentially use Apollo's query planner (JavaScript, but soon also in Rust) to generate a Query Plan, that you will execute in Python, but is it worth the effort when you have so many options that have good plugin system?