How a price is written on the storefront: From €40.00 /hour.

Two independent decorations, both optional and both off by default:

• a unit — free text per language ("per hour", "/m²", "в час"), so a service shop can state its pricing model. Free text rather than a vocabulary: nothing here needs to know what an hour is, and every shop invents units the next one has never heard of.

• a "From" prefix — set explicitly by the admin, or implied when the product's options genuinely produce a price range.

Storage

Both live under one reserved key in Product.metadata:

%{"_price_display" => %{
    "unit" => %{"en" => "per hour", "ru" => "в час"},
    "from" => true
  }}

A single versioned namespace rather than two loose top-level keys: the metadata map is an advertised extension point, so this module's data stays in one place that can grow (and be recognised) without colliding with whatever a host already stores there. _-prefixed matches the existing _option_values / _price_modifiers convention, and option keys may not begin with _, so no user-defined option can shadow it.

Context is load-bearing

render/4 takes a context because the same product means different things on different pages:

• :catalog — the product's asking price. May show "From", and the amount comes from the product's option-aware range.
• :selected — the price for the options the shopper picked. Exact, so never "From"; keeps the unit.
• :cart / :order — a SNAPSHOT of what was (or will be) charged. Exact, never "From", and the unit comes from the snapshot rather than the live product, so an edit or deletion cannot rewrite a line the customer already agreed to.

Absent data renders exactly what the module rendered before this existed.