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 (
    1859, 1854, 1923, 1858, 1922, 1855, 1920, 
    1469, 344, 1850, 1551, 284, 1885, 1628, 
    1625, 1475, 1276, 1312, 1303, 74, 1161, 
    75, 182, 161
  ) 
  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 0.00126

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_prices",
      "access_type": "range",
      "possible_keys": ["usergroup", "product_id", "lower_limit", "usergroup_id"],
      "key": "product_id",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 28,
      "filtered": 4.897957802,
      "index_condition": "cscart_product_prices.product_id in (1859,1854,1923,1858,1922,1855,1920,1469,344,1850,1551,284,1885,1628,1625,1475,1276,1312,1303,74,1161,75,182,161)",
      "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}