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 (
    111882, 111881, 111880, 111878, 112552, 
    111863, 111845, 114692, 114691, 114690, 
    114689, 112371, 112370, 112369, 112017, 
    112010, 111861, 111860, 111859, 111858
  ) 
  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 0.00067

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
111845 1.69000000
111858 1.69000000
111859 1.69000000
111860 1.69000000
111861 1.69000000
111863 1.69000000
111878 1.69000000
111880 1.69000000
111881 1.69000000
111882 1.69000000
112010 1.69000000
112017 1.69000000
112369 1.69000000
112370 1.69000000
112371 1.69000000
112552 1.69000000
114689 1.69000000
114690 1.69000000
114691 1.69000000
114692 1.69000000