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 (
    94159, 94158, 94157, 94156, 94155, 94154, 
    94153, 94152, 94151, 94150, 94149, 
    94148, 94147, 94145, 94144, 94143, 
    94142, 94808, 94590, 94588
  ) 
  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 0.00103

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
94142 1.69000000
94143 1.69000000
94144 1.69000000
94145 1.69000000
94147 1.69000000
94148 1.69000000
94149 1.69000000
94150 1.69000000
94151 1.69000000
94152 1.69000000
94153 1.69000000
94154 1.69000000
94155 1.69000000
94156 1.69000000
94157 1.69000000
94158 1.69000000
94159 1.69000000
94588 1.69000000
94590 1.69000000
94808 1.69000000