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 (
    76145, 76144, 76143, 76142, 76141, 76140, 
    76139, 76138, 76137, 76136, 76135, 
    76134, 76133, 76132, 76095, 77060, 
    76155, 76523, 76522, 76489
  ) 
  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 0.00055

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
76095 1.69000000
76132 1.69000000
76133 1.69000000
76134 1.69000000
76135 1.69000000
76136 1.69000000
76137 1.69000000
76138 1.69000000
76139 1.69000000
76140 1.69000000
76141 1.69000000
76142 1.69000000
76143 1.69000000
76144 1.69000000
76145 1.69000000
76155 1.69000000
76489 1.69000000
76522 1.69000000
76523 1.69000000
77060 1.69000000