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 (
    101123, 101122, 101121, 101120, 101119, 
    101118, 101117, 101116, 101115, 101114, 
    101113, 101112, 101111, 101110, 101109, 
    101071, 101070, 101069, 101068, 101067
  ) 
  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 40 Using where

Result

product_id price
101067 1.69000000
101068 1.69000000
101069 1.69000000
101070 1.69000000
101071 1.69000000
101109 1.69000000
101110 1.69000000
101111 1.69000000
101112 1.69000000
101113 1.69000000
101114 1.69000000
101115 1.69000000
101116 1.69000000
101117 1.69000000
101118 1.69000000
101119 1.69000000
101120 1.69000000
101121 1.69000000
101122 1.69000000
101123 1.69000000