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 (
    98892, 100136, 100131, 100045, 100011, 
    100035, 100010, 100009, 100002, 100001, 
    99991, 99966, 99863, 99862, 99436, 
    99430, 99427, 99280, 98828, 92941
  ) 
  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 0.00064

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
92941 1.69000000
98828 1.69000000
98892 1.69000000
99280 1.69000000
99427 1.69000000
99430 1.69000000
99436 1.69000000
99862 1.69000000
99863 1.69000000
99966 1.69000000
99991 1.69000000
100001 1.69000000
100002 1.69000000
100009 1.69000000
100010 1.69000000
100011 1.69000000
100035 1.69000000
100045 1.69000000
100131 1.69000000
100136 1.69000000