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 (
    97107, 92929, 97862, 98142, 98141, 98140, 
    98083, 98082, 98081, 98080, 98079, 
    98071, 98069, 98028, 98027, 98026, 
    98025, 98024, 98023, 98022
  ) 
  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 0.00059

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
92929 1.69000000
97107 1.69000000
97862 1.69000000
98022 1.69000000
98023 1.69000000
98024 1.69000000
98025 1.69000000
98026 1.69000000
98027 1.69000000
98028 1.69000000
98069 1.69000000
98071 1.69000000
98079 1.69000000
98080 1.69000000
98081 1.69000000
98082 1.69000000
98083 1.69000000
98140 1.69000000
98141 1.69000000
98142 1.69000000