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 (
    105210, 105209, 105250, 105249, 105248, 
    105247, 105246, 105245, 105244, 105243, 
    105242, 105241, 105240, 105208, 105207, 
    105206, 105205, 105204, 105203, 105202
  ) 
  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 0.00069

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
105202 1.69000000
105203 1.69000000
105204 1.69000000
105205 1.69000000
105206 1.69000000
105207 1.69000000
105208 8.99000000
105209 1.69000000
105210 1.69000000
105240 1.69000000
105241 1.69000000
105242 1.69000000
105243 1.69000000
105244 1.69000000
105245 1.69000000
105246 1.69000000
105247 1.69000000
105248 1.69000000
105249 1.69000000
105250 8.99000000