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 (
    191, 192, 193, 194, 195, 226, 227, 228, 
    229, 230, 231, 232, 264, 265, 266, 267, 
    268, 269, 270, 318, 319, 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
  ) 
  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 (191,192,193,194,195,226,227,228,229,230,231,232,264,265,266,267,268,269,270,318,319,320,321,322,323,3961,3962,3963,3964,3965,3966,3967,4006,4007,4008,4009,4010,4011,4012,4066,4067,4068,4069,4070,4071,4072,4073,4074))",
        "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)))"
      }
    }
  }
}