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 (
    10921, 10922, 10923, 10924, 10925, 10926, 
    10927, 10928, 10929, 10930, 10931, 
    10932, 10933, 10934, 10935, 10936, 
    10937, 10938, 10939, 10940, 10941, 
    10942, 10943, 10965, 10985, 11005, 
    11027, 11047, 11067, 11089, 11111, 
    11133, 11153, 11173, 11195, 11215, 
    11237, 11259, 11279, 11299, 11813, 
    11819, 11825, 11831, 11838, 11844, 
    11851, 11869, 11887, 11909, 11929, 
    11936, 11940, 11944, 11951, 11958, 
    11959, 11960, 11961, 11962, 11963, 
    11964, 11965, 12030, 12031, 12032, 
    12033, 12034, 12035, 12036, 12037, 
    12102, 12116, 12118, 12132, 12146, 
    12160, 12174, 12188, 12202, 8203, 8214, 
    8215, 8216, 8217, 8218, 8205, 8206, 
    8207, 8208, 8209, 8210, 8211, 8212
  ) 
  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 0.00321

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "71.66"
    },
    "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": 107,
        "rows_produced_per_join": 21,
        "filtered": "20.00",
        "index_condition": "(`gaseus`.`cscart_product_prices`.`product_id` in (10921,10922,10923,10924,10925,10926,10927,10928,10929,10930,10931,10932,10933,10934,10935,10936,10937,10938,10939,10940,10941,10942,10943,10965,10985,11005,11027,11047,11067,11089,11111,11133,11153,11173,11195,11215,11237,11259,11279,11299,11813,11819,11825,11831,11838,11844,11851,11869,11887,11909,11929,11936,11940,11944,11951,11958,11959,11960,11961,11962,11963,11964,11965,12030,12031,12032,12033,12034,12035,12036,12037,12102,12116,12118,12132,12146,12160,12174,12188,12202,8203,8214,8215,8216,8217,8218,8205,8206,8207,8208,8209,8210,8211,8212))",
        "cost_info": {
          "read_cost": "69.52",
          "eval_cost": "2.14",
          "prefix_cost": "71.66",
          "data_read_per_join": "513"
        },
        "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)))"
      }
    }
  }
}

Result

product_id price
8203 0.00000000
8205 100.00000000
8206 100.00000000
8207 100.00000000
8208 100.00000000
8209 100.00000000
8210 100.00000000
8211 100.00000000
8212 100.00000000
8214 100.00000000
8215 100.00000000
8216 100.00000000
8217 100.00000000
8218 100.00000000
10921 0.00000000
10922 0.00000000
10923 0.00000000
10924 0.00000000
10925 0.00000000
10926 0.00000000
10927 0.00000000
10928 0.00000000
10929 0.00000000
10930 0.00000000
10931 0.00000000
10932 0.00000000
10933 0.00000000
10934 0.00000000
10935 0.00000000
10936 0.00000000
10937 0.00000000
10938 0.00000000
10939 0.00000000
10940 0.00000000
10941 0.00000000
10942 0.00000000
10943 0.00000000
10965 0.00000000
10985 0.00000000
11005 0.00000000
11027 0.00000000
11047 0.00000000
11067 0.00000000
11089 0.00000000
11111 0.00000000
11133 0.00000000
11153 0.00000000
11173 0.00000000
11195 0.00000000
11215 0.00000000
11237 0.00000000
11259 0.00000000
11279 0.00000000
11299 0.00000000
11813 0.00000000
11819 0.00000000
11825 0.00000000
11831 0.00000000
11838 0.00000000
11844 0.00000000
11851 0.00000000
11869 0.00000000
11887 0.00000000
11909 0.00000000
11929 0.00000000
11936 0.00000000
11940 0.00000000
11944 0.00000000
11951 0.00000000
11958 0.00000000
11959 0.00000000
11960 0.00000000
11961 0.00000000
11962 0.00000000
11963 0.00000000
11964 0.00000000
11965 0.00000000
12030 0.00000000
12031 0.00000000
12032 0.00000000
12033 0.00000000
12034 0.00000000
12035 0.00000000
12036 0.00000000
12037 0.00000000
12102 0.00000000
12116 0.00000000
12118 0.00000000
12132 0.00000000
12146 0.00000000
12160 0.00000000
12174 0.00000000
12188 0.00000000
12202 0.00000000