Weekly Rental - Google Structured Data

Question

I have a site offering a product for weekly rent. All prices displayed are weekly.

I'm adding Google structured data to each page and trying to work out how to show that an offer is a weekly payment. ref: https://schema.org/Offer

Code is in PHP, it gets json_encoded and echoed out as json.

"offers" => [
    "@type" => "Offer",
    "availability" => "https://schema.org/InStock",
    "price" => "80.00",
    "priceCurrency" => "NZD"
],

do I use a https://schema.org/PriceSpecification?

But even that doesn't allow for additional payments.

Or is the price on its own ok because the humans who eventually read it will understand?