Structured Data layout for complex pricing structure - schema.org

Question

I'm working with products that have pricing structures based on bulk-buy offers. For example, the pricing for a product may be as follows:
Buy 10-19 and the value of 1 is $3
Buy 20-29 and the value of 1 is $2
Buy 30-39 and the value of 1 is $1
Buy 40 or more and the value of 1 is $0.50
Minimum quantity available to purchase is 10.
How can I mark this up properly in structured data (Microdata format)?
Currently I have:
<span itemprop="offers" itemscope itemtype="http://schema.org/Offer">
<meta itemprop="priceCurrency" content="USD"/>
<meta itemprop="price" content="3" />
<span itemprop="eligibleQuantity" itemscope itemtype="http://schema.org/QuantitativeValue">
<meta itemprop="minValue" content="10" />
<meta itemprop="maxValue" content="19" />
<meta itemprop="value" content="Number" />
</span>
</span>
For each variant. Then I have:
<span itemprop="priceSpecification">
<span itemprop="eligibleQuantity" itemscope itemtype="http://schema.org/QuantitativeValue">
<meta itemprop="minValue" content="10" />
</span>
</span>
On the product block itself, to indicate the minimum quantity of 10.
I'm really not at all confident this is the right structure and tags to use. Could anybody lend some insight?

Answer 1

You are missing the actual PriceSpecification items (as values for the priceSpecification property). UnitPriceSpecification seems to be the appropriate sub-type in your case.
So the structure could look like this:
<div itemscope itemtype="http://schema.org/Offer">
<div itemprop="priceSpecification" itemscope itemtype="http://schema.org/UnitPriceSpecification"></div>
<div itemprop="priceSpecification" itemscope itemtype="http://schema.org/UnitPriceSpecification"></div>
<div itemprop="priceSpecification" itemscope itemtype="http://schema.org/UnitPriceSpecification"></div>
</div>
Personally I would provide a UnitPriceSpecification for the first level (10-19), too, instead of providing its properties directly under Offer:
<div itemprop="priceSpecification" itemscope itemtype="http://schema.org/UnitPriceSpecification">
<p itemprop="eligibleQuantity" itemscope itemtype="http://schema.org/QuantitativeValue">
<span itemprop="minValue">10</span>-<span itemprop="maxValue">19</span>
</p>
<p>$<span itemprop="price">3</span> <meta itemprop="priceCurrency" content="USD"/></p>
</div>
But I don’t know if there aren’t some consumers out there that might expect it directly under Offer.