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 (
    502, 27002, 46548, 23017, 26889, 44858, 
    26897, 23047, 26876, 40441, 5994, 4512, 
    42111, 26893, 26878, 26888, 26885, 
    26875, 37095, 26881, 26879, 26884, 
    26883, 34676, 40439, 34673, 1718, 31629, 
    37314, 5781, 41205, 40434
  ) 
  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 0.00167

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "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": 32,
          "filtered": 99.9960556,
          "index_condition": "cscart_product_prices.product_id in (502,27002,46548,23017,26889,44858,26897,23047,26876,40441,5994,4512,42111,26893,26878,26888,26885,26875,37095,26881,26879,26884,26883,34676,40439,34673,1718,31629,37314,5781,41205,40434)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}