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 (
    13944, 13909, 14031, 14025, 13924, 13921, 
    13857, 13859, 13858, 13897, 14030, 
    14029, 13866, 13908, 14021, 13894, 
    13969, 14019, 13951, 13873, 13974, 
    13989, 13930, 13938
  ) 
  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 0.00051

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.06190128,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_prices",
          "access_type": "range",
          "possible_keys": [
            "usergroup",
            "product_id",
            "lower_limit",
            "usergroup_id"
          ],
          "key": "usergroup",
          "key_length": "9",
          "used_key_parts": ["product_id", "usergroup_id", "lower_limit"],
          "loops": 1,
          "rows": 48,
          "cost": 0.04656984,
          "filtered": 49.95571136,
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.product_id in (13944,13909,14031,14025,13924,13921,13857,13859,13858,13897,14030,14029,13866,13908,14021,13894,13969,14019,13951,13873,13974,13989,13930,13938) and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}