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 (
    2133, 2508, 18260, 33747, 2966, 263, 
    31628, 3877, 6615, 5894, 2135, 6056, 
    2507, 2591, 2501, 1710, 2284, 19285, 
    5568, 3879, 4305, 2652, 23419, 3749, 
    31641, 2510, 2237, 1881, 400, 2963, 
    6533, 46734
  ) 
  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 0.00509

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 (2133,2508,18260,33747,2966,263,31628,3877,6615,5894,2135,6056,2507,2591,2501,1710,2284,19285,5568,3879,4305,2652,23419,3749,31641,2510,2237,1881,400,2963,6533,46734)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}