The "price_range" value is assigned by Shopify based on one of its possible preset values rather than the exact range of your variants' prices.
The possible values for this attribute are `0:10`, `10:25`, `25:50`, `50:75`, `75:100`, `100:150`, and so on.
For example, let's say your product has three different variants:
Variant A - $50
Variant B - $60
Variant C - $65
Since the product's variants' prices are between $50 and $65, the product's price range falls into `50:75`. Therefore, it is indexed with the "price_range" value of `50:75.`