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 (
    35839, 35731, 631, 4367, 5455, 5581, 
    5577, 35869, 5461, 5958, 5476, 33631, 
    5959, 5472, 5457, 5462, 5960, 5957, 
    5961, 16802, 35733, 5448, 4363, 5956, 
    5451, 5963, 5447, 4365, 5469, 4468, 
    5464, 5474
  ) 
  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 0.00529

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 (35839,35731,631,4367,5455,5581,5577,35869,5461,5958,5476,33631,5959,5472,5457,5462,5960,5957,5961,16802,35733,5448,4363,5956,5451,5963,5447,4365,5469,4468,5464,5474)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}