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 (
    112229, 112228, 112227, 112226, 112225, 
    112224, 112223, 112134, 112133, 112132, 
    112131, 112130, 112129, 112128, 112127, 
    112126, 112125, 112124, 112236, 112235
  ) 
  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 0.00105

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
112124 1.69000000
112125 1.69000000
112126 1.69000000
112127 1.69000000
112128 1.69000000
112129 1.69000000
112130 1.69000000
112131 1.69000000
112132 1.69000000
112133 1.69000000
112134 1.69000000
112223 1.69000000
112224 1.69000000
112225 1.69000000
112226 1.69000000
112227 1.69000000
112228 1.69000000
112229 1.69000000
112235 1.69000000
112236 1.69000000