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 (
    6368, 3519, 15322, 6274, 48559, 30368, 
    48251, 40381, 47828, 46583, 48557, 
    1945, 48244, 22263, 48503, 2859, 35177, 
    44946, 44943, 1977, 3578, 44944, 27356, 
    35167, 35165, 35174, 35176, 35173, 
    35170, 2291, 35172, 35171
  ) 
  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 0.00818

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 (6368,3519,15322,6274,48559,30368,48251,40381,47828,46583,48557,1945,48244,22263,48503,2859,35177,44946,44943,1977,3578,44944,27356,35167,35165,35174,35176,35173,35170,2291,35172,35171)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}