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 (
    926, 1266, 26856, 26851, 41418, 37302, 
    32360, 37284, 41368, 1542, 3464, 4865, 
    6103, 26857, 41387, 41423, 5635, 31645, 
    41367, 2259, 37942, 2449, 31904, 31618, 
    41134, 6102, 4793, 41102, 36494, 41428, 
    37289, 2248
  ) 
  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 0.01072

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 (926,1266,26856,26851,41418,37302,32360,37284,41368,1542,3464,4865,6103,26857,41387,41423,5635,31645,41367,2259,37942,2449,31904,31618,41134,6102,4793,41102,36494,41428,37289,2248)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}