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 (
    112062, 112061, 112060, 112059, 112058, 
    112057, 112056, 112055, 112054, 112052, 
    112051, 112435, 112434, 112290, 112289, 
    112536, 112535, 112534, 112533, 112532
  ) 
  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 0.00064

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
112051 1.69000000
112052 1.69000000
112054 1.69000000
112055 1.69000000
112056 1.69000000
112057 1.69000000
112058 1.69000000
112059 1.69000000
112060 1.69000000
112061 1.69000000
112062 1.69000000
112289 1.69000000
112290 1.69000000
112434 1.69000000
112435 1.69000000
112532 1.69000000
112533 1.69000000
112534 1.69000000
112535 1.69000000
112536 1.69000000