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 (
    92732, 92731, 92730, 92729, 92728, 92726, 
    92725, 92723, 92721, 92720, 92719, 
    92718, 92717, 92716, 92715, 92713, 
    92712, 92711, 92710, 92709
  ) 
  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 0.00076

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
92709 1.69000000
92710 1.69000000
92711 1.69000000
92712 1.69000000
92713 1.69000000
92715 1.69000000
92716 1.69000000
92717 1.69000000
92718 1.69000000
92719 1.69000000
92720 1.69000000
92721 1.69000000
92723 1.69000000
92725 1.69000000
92726 1.69000000
92728 1.69000000
92729 1.69000000
92730 1.69000000
92731 1.69000000
92732 1.69000000