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 (
    40808, 37295, 5772, 351, 4887, 2565, 
    37298, 1052, 1850, 37486, 2155, 6527, 
    26858, 26848, 5759, 47592, 2626, 406, 
    6526, 26862, 3621, 41130, 31622, 4889, 
    37280, 31902, 21746, 2250, 35466, 26863, 
    43796, 1051
  ) 
  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 0.00591

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 (40808,37295,5772,351,4887,2565,37298,1052,1850,37486,2155,6527,26858,26848,5759,47592,2626,406,6526,26862,3621,41130,31622,4889,37280,31902,21746,2250,35466,26863,43796,1051)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}