Pricing suitable for small teams, and perhaps even a free tier, is absolutely on the roadmap. We decided to build the "hard", security-obsessed version of the infrastructure first -- single-tenant, with dedicated and physically isolated hardware and networking for every customer. That means there's a bit of per-customer overhead that we have to recoup.
In the future, we will probably have a multi-tenant offering that's easier for open source projects to adopt. In the meantime, if your project is cool and would benefit from our testing, you can try to get our research team interested in using it as part of the curriculum that makes our platform smarter.
Disclosure: I'm an Antithesis co-founder.