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 (
    391789, 265231, 81619, 285940, 81632, 
    271489, 81662, 339530, 265039, 265034, 
    285937, 271497, 387095, 81615, 392212, 
    285942, 339446, 271493, 81639, 271504, 
    265258, 81706, 265031, 339514, 264987, 
    265041, 265261, 265263, 339551, 271500, 
    339521, 286476, 81649, 264988, 285945, 
    271506, 265244, 265256, 271496, 271492, 
    339501, 151897, 339499, 285939, 339495, 
    339721, 366887, 392150, 81622, 392214, 
    392215, 265038, 81652, 271498, 81697, 
    339494, 265242, 339503, 339531, 224456, 
    81693, 339516, 285938, 81660, 271510, 
    359818, 285943, 271503, 339539, 285941, 
    339447, 339509, 81669, 271494, 264989, 
    285946, 264990, 271502, 265232, 265254, 
    339636, 285966, 285970, 114755, 339637, 
    339492, 285968, 339538, 369244, 271490, 
    339506, 265250, 265001, 265237, 271505, 
    339724, 392179, 339635, 81628, 339502
  ) 
  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 0.00165

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 (391789,265231,81619,285940,81632,271489,81662,339530,265039,265034,285937,271497,387095,81615,392212,285942,339446,271493,81639,271504,265258,81706,265031,339514,264987,265041,265261,265263,339551,271500,339521,286476,81649,264988,285945,271506,265244,265256,271496,271492,339501,151897,339499,285939,339495,339721,366887,392150,81622,392214,392215,265038,81652,271498,81697,339494,265242,339503,339531,224456,81693,339516,285938,81660,271510,359818,285943,271503,339539,285941,339447,339509,81669,271494,264989,285946,264990,271502,265232,265254,339636,285966,285970,114755,339637,339492,285968,339538,369244,271490,339506,265250,265001,265237,271505,339724,392179,339635,81628,339502)) and (`webmarco`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}