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 (
    26868, 46144, 44931, 6165, 28238, 26867, 
    46142, 46145, 44930, 46148, 6148, 47898, 
    46149, 41952, 46147, 47165, 47166, 
    47897, 41955, 47167, 47668, 46146, 
    43662, 41954, 47664, 47168, 47665, 
    49394, 41953, 47667, 16567, 41956
  ) 
  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 0.00171

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 (26868,46144,44931,6165,28238,26867,46142,46145,44930,46148,6148,47898,46149,41952,46147,47165,47166,47897,41955,47167,47668,46146,43662,41954,47664,47168,47665,49394,41953,47667,16567,41956)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}