Replace CASE WHEN statement with something more sensible
COALESCE(…, …, 2147483647) will never return NULL.  Furthermore, MIN(…) will only return NULL when all of its inputs are NULL.

Assuming that every NewPrice and every Price is at most 2147483647, the following query should be equivalent.

SELECT COUNT(*)
     , ISNULL(MIN(COALESCE(NewPrice, Price)), 0)
    FROM MerchantsProducts