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 (
    99275, 99272, 99262, 99261, 99258, 99217, 
    99132, 99129, 99124, 98903, 98630, 
    98626, 98625, 98566, 97667, 99274, 
    89234, 99131, 98519, 99123
  ) 
  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 0.00058

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
89234 1.69000000
97667 1.69000000
98519 1.69000000
98566 1.69000000
98625 1.69000000
98626 1.69000000
98630 1.69000000
98903 1.69000000
99123 1.69000000
99124 1.69000000
99129 1.69000000
99131 1.69000000
99132 1.69000000
99217 1.69000000
99258 1.69000000
99261 1.69000000
99262 1.69000000
99272 1.69000000
99274 1.69000000
99275 1.69000000