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 (
    27946, 3525, 3523, 2949, 3534, 1404, 
    33606, 2936, 2968, 5777, 2944, 5776, 
    32317, 2919, 3019, 2868, 37849, 1407, 
    2864, 3408, 3412, 1417, 32328, 3025, 
    1406, 32360, 3409, 19210, 27927, 35733, 
    32319, 1419
  ) 
  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 0.00213

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 (27946,3525,3523,2949,3534,1404,33606,2936,2968,5777,2944,5776,32317,2919,3019,2868,37849,1407,2864,3408,3412,1417,32328,3025,1406,32360,3409,19210,27927,35733,32319,1419)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}