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 (
    6418, 6419, 6420, 6421, 2823, 2824, 2825, 
    2826, 6408, 6409, 6410, 6411, 6412, 
    2827, 2828, 2829, 2830, 2831, 6413, 
    6414, 6415, 6416, 2928, 2929, 2930, 
    2931, 2932, 6513, 6514, 6515, 6516, 
    3032, 6609, 3028, 3029, 3030, 3031, 
    6605, 6606, 6607, 6608, 6610, 6611, 
    6612, 6613, 3024, 3025, 3026, 3027, 
    3301, 6847, 3300, 2841, 2842, 2843, 
    2844, 6426, 6427, 6428, 6429, 6430, 
    2765, 2766, 2767, 2768, 6352, 6353, 
    6354, 6355, 6356, 2185, 2186, 2187, 
    2188, 5785, 5786, 5787, 5788, 5789, 
    6641, 6219, 5807, 3722, 5819, 1516, 
    6623, 1504, 1494, 6209, 1499, 1489, 
    1433, 6614, 2268, 2269, 2270
  ) 
  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 0.00137

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "67.21"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "range",
        "possible_keys": [
          "usergroup",
          "product_id",
          "lower_limit",
          "usergroup_id"
        ],
        "key": "product_id",
        "used_key_parts": [
          "product_id"
        ],
        "key_length": "3",
        "rows_examined_per_scan": 96,
        "rows_produced_per_join": 19,
        "filtered": "20.00",
        "index_condition": "(`gaseus`.`cscart_product_prices`.`product_id` in (6418,6419,6420,6421,2823,2824,2825,2826,6408,6409,6410,6411,6412,2827,2828,2829,2830,2831,6413,6414,6415,6416,2928,2929,2930,2931,2932,6513,6514,6515,6516,3032,6609,3028,3029,3030,3031,6605,6606,6607,6608,6610,6611,6612,6613,3024,3025,3026,3027,3301,6847,3300,2841,2842,2843,2844,6426,6427,6428,6429,6430,2765,2766,2767,2768,6352,6353,6354,6355,6356,2185,2186,2187,2188,5785,5786,5787,5788,5789,6641,6219,5807,3722,5819,1516,6623,1504,1494,6209,1499,1489,1433,6614,2268,2269,2270))",
        "cost_info": {
          "read_cost": "65.29",
          "eval_cost": "1.92",
          "prefix_cost": "67.21",
          "data_read_per_join": "460"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`gaseus`.`cscart_product_prices`.`lower_limit` = 1) and (`gaseus`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}