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 (
    320, 321, 322, 323, 3961, 3962, 3963, 
    3964, 3965, 3966, 3967, 4006, 4007, 
    4008, 4009, 4010, 4011, 4012, 4066, 
    4067, 4068, 4069, 4070, 4071, 4072, 
    4073, 4074, 4075, 4076, 4077, 4078, 
    4079, 4110, 4111, 4112, 4113, 4114, 
    4115, 4116, 4149, 4150, 4151, 4152, 
    4153, 4154, 4155, 4202, 4203
  ) 
  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 0.00152

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": "19.99",
        "index_condition": "(`test2_gaseus`.`cscart_product_prices`.`product_id` in (320,321,322,323,3961,3962,3963,3964,3965,3966,3967,4006,4007,4008,4009,4010,4011,4012,4066,4067,4068,4069,4070,4071,4072,4073,4074,4075,4076,4077,4078,4079,4110,4111,4112,4113,4114,4115,4116,4149,4150,4151,4152,4153,4154,4155,4202,4203))",
        "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": "((`test2_gaseus`.`cscart_product_prices`.`lower_limit` = 1) and (`test2_gaseus`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}