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 (
    97698, 97697, 97696, 97695, 97669, 97655, 
    97558, 97393, 96323, 96738, 89235, 
    97593, 97584, 97095, 97094, 97582, 
    97562, 97561, 97511, 94776
  ) 
  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 0.00052

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
89235 1.69000000
94776 1.69000000
96323 1.69000000
96738 1.69000000
97094 1.69000000
97095 1.69000000
97393 1.69000000
97511 1.69000000
97558 1.69000000
97561 1.69000000
97562 1.69000000
97582 1.69000000
97584 1.69000000
97593 1.69000000
97655 1.69000000
97669 1.69000000
97695 1.69000000
97696 1.69000000
97697 1.69000000
97698 1.69000000