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
  ) 
  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 0.00128

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "33.61"
    },
    "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": 48,
        "rows_produced_per_join": 9,
        "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))",
        "cost_info": {
          "read_cost": "32.65",
          "eval_cost": "0.96",
          "prefix_cost": "33.61",
          "data_read_per_join": "230"
        },
        "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
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