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 (
    92453, 92452, 92451, 1643, 92832, 92831, 
    92670, 92669, 92275, 92274, 92272, 
    92271, 92270, 92269, 92268, 92061, 
    92008, 91998, 92557, 92500
  ) 
  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 0.00070

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
1643 1.69000000
91998 1.69000000
92008 1.69000000
92061 1.69000000
92268 1.69000000
92269 1.69000000
92270 1.69000000
92271 1.69000000
92272 1.69000000
92274 1.69000000
92275 1.69000000
92451 1.69000000
92452 1.69000000
92453 1.69000000
92500 1.69000000
92557 1.69000000
92669 1.69000000
92670 1.69000000
92831 1.69000000
92832 1.69000000