SELECT 
  cscart_product_prices.product_id, 
  MIN(
    IF(
      cscart_product_prices.percentage_discount = 0, 
      cscart_product_prices.price, 
      cscart_product_prices.price - (
        cscart_product_prices.price * cscart_product_prices.percentage_discount
      )/ 100
    )
  ) AS price 
FROM 
  cscart_product_prices 
WHERE 
  cscart_product_prices.product_id IN (
    103946, 103945, 103944, 103943, 103942, 
    103941, 103940, 103939, 103938, 103937
  ) 
  AND cscart_product_prices.lower_limit = 1 
  AND cscart_product_prices.usergroup_id IN (0, 1) 
GROUP BY 
  cscart_product_prices.product_id

Query time 0.00043

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_product_prices range usergroup,product_id,lower_limit,usergroup_id usergroup 9 20 Using where

Result

product_id price
103937 1.69000000
103938 1.69000000
103939 1.69000000
103940 1.69000000
103941 1.69000000
103942 1.69000000
103943 1.69000000
103944 1.69000000
103945 1.69000000
103946 1.69000000