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 (
    93059, 93057, 92492, 92956, 92883, 92900, 
    92899, 92898, 92897, 92895, 92834, 
    92808, 92789, 92788, 92765, 92758, 
    92675, 92673, 92291, 92238
  ) 
  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 0.00108

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
92238 1.69000000
92291 1.69000000
92492 1.69000000
92673 1.69000000
92675 1.69000000
92758 1.69000000
92765 1.69000000
92788 1.69000000
92789 1.69000000
92808 1.69000000
92834 1.69000000
92883 1.69000000
92895 1.69000000
92897 1.69000000
92898 1.69000000
92899 1.69000000
92900 1.69000000
92956 1.69000000
93057 1.69000000
93059 1.69000000