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 (
    105308, 105307, 105306, 105305, 105304, 
    105303, 105302, 105301, 105300, 105299, 
    105298
  ) 
  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 0.00065

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 22 Using where

Result

product_id price
105298 1.69000000
105299 1.69000000
105300 1.69000000
105301 1.69000000
105302 1.69000000
105303 1.69000000
105304 1.69000000
105305 1.69000000
105306 1.69000000
105307 1.69000000
105308 1.69000000