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 (
    35732, 35855, 35856, 35857, 35858, 35859, 
    35860, 35861, 35862, 35863, 35864, 
    35865, 35866, 35867, 35868, 35869, 
    35870, 35871, 35872, 35873, 35874, 
    35875, 35876, 35877, 35878
  ) 
  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 0.00119

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": 25,
          "filtered": 99.9960556,
          "index_condition": "cscart_product_prices.product_id in (35732,35855,35856,35857,35858,35859,35860,35861,35862,35863,35864,35865,35866,35867,35868,35869,35870,35871,35872,35873,35874,35875,35876,35877,35878)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}