opam is maintained by OCamlPro, why not contact them and get a quote ? It
won't be 300$, but everybody will enjoy the feature in the next version.

As a side note, a long time ago, I had an implementation of a binary cache
for OPAM. The modifications in OPAM were minimal: opam would
just call a hook to build the package and install it, providing a checksum
of dependencies and sources. The checksum would be used by an external tool
(`ocp-bin`) to query the local binary cache (or a remote server) and either
re-install the package or build it and save it in the cache. Since it was
written in 2013, not sure if it would still work easily with current opam.
Its code was used later to create opam-builder.
--
Fabrice LE FESSANT
CEO Origin-Labs SAS & Dune Network

Le jeu. 18 juin 2020 à 03:53, Francois Berenger <mlists@ligand.eu> a écrit :

> Cf.
> https://discuss.ocaml.org/t/bounty-for-compilation-cache-in-opam/2482
> for details.
>
-- 
Fabrice LE FESSANT
Chercheur en Informatique
INRIA Paris Rocquencourt -- OCamlPro
Programming Languages and Distributed Systems