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 (
    265000, 40404, 262379, 265262, 392209, 
    339537, 114747, 271509, 339493, 265255, 
    339524, 339540, 339536, 339491, 265241, 
    114761, 265230, 339517, 339522, 339526, 
    339520, 285971, 81644, 265236, 81606, 
    81700, 271508, 265251, 271499, 224457, 
    271501, 339490, 392218, 265238, 265240, 
    392216, 265253, 392217, 81601, 366896, 
    339741, 381654, 265243, 265264, 81687, 
    339498, 271507, 339449, 265233, 32880, 
    339528, 224454, 381657, 81703, 391799, 
    265234, 265257, 381658, 339497, 339689, 
    224455, 265259, 285967, 81679, 339448, 
    265249, 265252, 339450, 265260, 359820, 
    339435, 392151, 265239, 285969, 381656, 
    339622, 339442, 381655, 81666, 339616, 
    339443, 152086, 339436, 170242, 339574, 
    259708, 339523, 339507, 205875, 339437, 
    339504, 339451, 339512, 265035, 81683, 
    139611, 339740, 339609, 339500, 339532
  ) 
  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 0.00181

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "280.31"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "range",
        "possible_keys": [
          "usergroup",
          "product_id",
          "lower_limit",
          "usergroup_id"
        ],
        "key": "usergroup",
        "used_key_parts": [
          "product_id",
          "usergroup_id",
          "lower_limit"
        ],
        "key_length": "9",
        "rows_examined_per_scan": 200,
        "rows_produced_per_join": 200,
        "filtered": "100.00",
        "cost_info": {
          "read_cost": "240.31",
          "eval_cost": "40.00",
          "prefix_cost": "280.31",
          "data_read_per_join": "12K"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`webmarco`.`cscart_product_prices`.`lower_limit` = 1) and (`webmarco`.`cscart_product_prices`.`product_id` in (265000,40404,262379,265262,392209,339537,114747,271509,339493,265255,339524,339540,339536,339491,265241,114761,265230,339517,339522,339526,339520,285971,81644,265236,81606,81700,271508,265251,271499,224457,271501,339490,392218,265238,265240,392216,265253,392217,81601,366896,339741,381654,265243,265264,81687,339498,271507,339449,265233,32880,339528,224454,381657,81703,391799,265234,265257,381658,339497,339689,224455,265259,285967,81679,339448,265249,265252,339450,265260,359820,339435,392151,265239,285969,381656,339622,339442,381655,81666,339616,339443,152086,339436,170242,339574,259708,339523,339507,205875,339437,339504,339451,339512,265035,81683,139611,339740,339609,339500,339532)) and (`webmarco`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}