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 (
    105261, 105260, 105259, 105258, 105257, 
    105256, 105255, 105254, 105253, 105252, 
    105251
  ) 
  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 0.00042

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
105251 1.69000000
105252 1.69000000
105253 1.69000000
105254 1.69000000
105255 1.69000000
105256 1.69000000
105257 1.69000000
105258 1.69000000
105259 1.69000000
105260 1.69000000
105261 1.69000000