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 (
    98753, 98752, 98751, 98750, 98749, 98624, 
    98427, 98939, 92935, 98907, 98906, 
    98905, 98904, 98902, 98832, 98831, 
    98795, 98623, 98615, 98435
  ) 
  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 0.00060

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
92935 1.69000000
98427 1.69000000
98435 1.69000000
98615 1.69000000
98623 1.69000000
98624 1.69000000
98749 1.69000000
98750 1.69000000
98751 1.69000000
98752 1.69000000
98753 1.69000000
98795 1.69000000
98831 1.69000000
98832 1.69000000
98902 1.69000000
98904 1.69000000
98905 1.69000000
98906 1.69000000
98907 1.69000000
98939 1.69000000