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 (
    98021, 98020, 98019, 98018, 98017, 98016, 
    98015, 98014, 97917, 97758, 97671, 
    97663, 97471, 97470, 97469, 97468, 
    97292, 97291, 97178, 89232
  ) 
  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 0.00068

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
89232 1.69000000
97178 1.69000000
97291 1.69000000
97292 1.69000000
97468 1.69000000
97469 1.69000000
97470 1.69000000
97471 1.69000000
97663 1.69000000
97671 1.69000000
97758 1.69000000
97917 1.69000000
98014 1.69000000
98015 1.69000000
98016 1.69000000
98017 1.69000000
98018 1.69000000
98019 1.69000000
98020 1.69000000
98021 1.69000000