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 (
    2532, 2533, 2534, 13416, 2357, 2807, 
    12976, 2305, 2304, 11806, 12980, 12740, 
    11117, 11787, 2587, 2588, 2591, 2590, 
    2553, 2589, 2581, 2592, 2576, 2685
  ) 
  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 0.00817

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "cscart_product_prices.product_id",
      "temporary_table": {
        "table": {
          "table_name": "cscart_product_prices",
          "access_type": "ref",
          "possible_keys": [
            "usergroup",
            "product_id",
            "lower_limit",
            "usergroup_id"
          ],
          "key": "lower_limit",
          "key_length": "3",
          "used_key_parts": ["lower_limit"],
          "ref": ["const"],
          "rows": 6449,
          "filtered": 4.592569828,
          "attached_condition": "cscart_product_prices.lower_limit <=> 1 and cscart_product_prices.product_id in (2532,2533,2534,13416,2357,2807,12976,2305,2304,11806,12980,12740,11117,11787,2587,2588,2591,2590,2553,2589,2581,2592,2576,2685) and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    }
  }
}