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 (
    34835, 37789, 39361, 34820, 40466, 40398, 
    40351, 38316, 39325, 40308, 39613, 
    38314, 37788, 36045, 39878, 39611, 
    39354, 39353, 39299, 39300, 39268, 
    38317, 39137, 39138, 39139, 39058, 
    38994, 39313, 37790, 38179
  ) 
  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 0.00070

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "74.81"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "range",
        "possible_keys": [
          "membership",
          "src_k",
          "product_id",
          "lower_limit",
          "membership_id"
        ],
        "key": "product_id",
        "used_key_parts": [
          "product_id"
        ],
        "key_length": "3",
        "rows_examined_per_scan": 32,
        "rows_produced_per_join": 6,
        "filtered": "19.89",
        "index_condition": "(`ea201_diorama`.`cscart_product_prices`.`product_id` in (34835,37789,39361,34820,40466,40398,40351,38316,39325,40308,39613,38314,37788,36045,39878,39611,39354,39353,39299,39300,39268,38317,39137,39138,39139,39058,38994,39313,37790,38179))",
        "cost_info": {
          "read_cost": "73.54",
          "eval_cost": "1.27",
          "prefix_cost": "74.81",
          "data_read_per_join": "152"
        },
        "used_columns": [
          "product_id",
          "price",
          "lower_limit",
          "usergroup_id",
          "percentage_discount"
        ],
        "attached_condition": "((`ea201_diorama`.`cscart_product_prices`.`lower_limit` = 1) and (`ea201_diorama`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}