Cutting down on the amount of (first:X) calls can definitely make it less expensive. You actually only need the first inventorylevel (which reduces the cost of the query to 10), rather than all of them since currently an item can only be stocked at either Shopify Locations or a FulfillmentService, not both.
Edit: scaling up to 30 variants costs 213, and 50 is 353, so not terrible.