How can I calculate a "stepped" price in SQL?

WITH prices As
(
    -- Not stepped:
    -- * Only a single price band should match;
    -- * Total price = quantity * price;
    SELECT
        l.licence_companyid,
        l.licence_productid,
        l.licence_quantity,
        b.pricing_price,
        b.pricing_price * l.licence_quantity As company_cost
    FROM
        licence As l
        INNER JOIN price_banding As b
        ON b.pricing_productid = l.licence_productid
    WHERE
        b.pricing_stepped = 0
    And 
        b.pricing_band_min <= l.licence_quantity
    And
        (b.pricing_band_max >= l.licence_quantity Or b.pricing_band_max Is Null)

    UNION ALL

    -- Stepped:
    -- * Match all price bands that apply (min < quantity);
    -- * Total price = sum of [quantity for this band] * price;
    SELECT
        l.licence_companyid,
        l.licence_productid,
        Max(l.licence_quantity),
        Max(b.pricing_price),
        Sum(b.pricing_price * CASE
            WHEN b.pricing_band_max Is Null THEN 1 + l.licence_quantity - b.pricing_band_min
            WHEN b.pricing_band_max >= l.licence_quantity THEN 1 + l.licence_quantity - b.pricing_band_min
            ELSE 1 + b.pricing_band_max - b.pricing_band_min
        END)
    FROM
        licence As l
        INNER JOIN price_banding As b
        ON b.pricing_productid = l.licence_productid
    WHERE
        b.pricing_stepped = 1
    And 
        b.pricing_band_min <= l.licence_quantity
    GROUP BY
        l.licence_companyid,
        l.licence_productid
)
SELECT
    c.company_id,
    c.company_name,
    b.pricing_price,
    p.product_name,
    b.licence_quantity,
    b.company_cost
FROM
    prices As b
    INNER JOIN company As c
    ON c.company_id = b.licence_companyid
    INNER JOIN product As p
    ON p.product_id = b.licence_productid
;