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 (
    394196, 114756, 81595, 265003, 149755, 
    264991, 262367, 286468, 387085, 265175, 
    80451, 262401, 387100, 387101, 277549, 
    286472, 277552, 265004, 262376, 265174, 
    277550, 286478, 277548, 387099, 149820, 
    81523, 286465, 277547, 387097, 387102, 
    149750, 286467, 339527, 264986, 286475, 
    391790, 387103, 286479, 359819, 286473, 
    286469, 391787, 391791, 31800, 286466, 
    435216, 286470, 391792, 286471, 277551, 
    391739, 286474, 286, 391740, 262374, 
    381645, 359629, 264695, 262391, 535, 
    359628, 381653, 391793, 381646, 381643, 
    391795, 392213, 225059, 387091, 391794, 
    387043, 264694, 262397, 264699, 381647, 
    391788, 391797, 381644, 339513, 391796, 
    282476, 151903, 381642, 81654, 387038, 
    339519, 81637, 282477, 264697, 264700, 
    339510, 339508, 265002, 339518, 339713, 
    339505, 265235, 339525, 81590, 262396
  ) 
  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 0.00229

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 (394196,114756,81595,265003,149755,264991,262367,286468,387085,265175,80451,262401,387100,387101,277549,286472,277552,265004,262376,265174,277550,286478,277548,387099,149820,81523,286465,277547,387097,387102,149750,286467,339527,264986,286475,391790,387103,286479,359819,286473,286469,391787,391791,31800,286466,435216,286470,391792,286471,277551,391739,286474,286,391740,262374,381645,359629,264695,262391,535,359628,381653,391793,381646,381643,391795,392213,225059,387091,391794,387043,264694,262397,264699,381647,391788,391797,381644,339513,391796,282476,151903,381642,81654,387038,339519,81637,282477,264697,264700,339510,339508,265002,339518,339713,339505,265235,339525,81590,262396)) and (`webmarco`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}