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 (
    315954, 323397, 325134, 14991, 85379, 
    276603, 279485, 301669, 302229, 304271, 
    311272, 311276, 311278, 315849, 315875, 
    315879, 315890, 315907, 315918, 315940, 
    316080, 316422, 323401, 325341, 254793, 
    292592, 299513, 299552, 301767, 312729, 
    315858, 315917, 315937, 315944, 315949, 
    316051, 316079, 316206, 64640, 293151, 
    296861, 305641, 307613, 311268, 311277, 
    314526, 315213, 315900, 315936, 316049, 
    323291, 324558, 324559, 325117, 325288, 
    133629, 265179, 273025, 298721, 306823, 
    307582, 311271, 315901, 315919, 315950, 
    316050, 323287, 323292, 323649, 200976, 
    300745, 311269, 312681, 312769, 315946, 
    323483, 325116, 301456, 307583, 311270
  ) 
  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 0.00392

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "72.08"
    },
    "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": 160,
        "rows_produced_per_join": 160,
        "filtered": "100.00",
        "cost_info": {
          "read_cost": "56.08",
          "eval_cost": "16.00",
          "prefix_cost": "72.08",
          "data_read_per_join": "5K"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`unicomps`.`cscart_product_prices`.`lower_limit` = 1) and (`unicomps`.`cscart_product_prices`.`product_id` in (315954,323397,325134,14991,85379,276603,279485,301669,302229,304271,311272,311276,311278,315849,315875,315879,315890,315907,315918,315940,316080,316422,323401,325341,254793,292592,299513,299552,301767,312729,315858,315917,315937,315944,315949,316051,316079,316206,64640,293151,296861,305641,307613,311268,311277,314526,315213,315900,315936,316049,323291,324558,324559,325117,325288,133629,265179,273025,298721,306823,307582,311271,315901,315919,315950,316050,323287,323292,323649,200976,300745,311269,312681,312769,315946,323483,325116,301456,307583,311270)) and (`unicomps`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}