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 (
    34828, 34928, 39919, 39920, 39921, 38856, 
    38600, 38601, 35779, 35599, 35600, 
    30985, 31040, 30389, 30968, 30969, 
    30971, 30972, 30974, 30976, 30977, 
    30986, 30989, 31041, 31045, 31046, 
    31047, 31048, 31051
  ) 
  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 0.00319

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "69.61"
    },
    "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": 29,
        "rows_produced_per_join": 5,
        "filtered": "19.89",
        "index_condition": "(`ea201_diorama`.`cscart_product_prices`.`product_id` in (34828,34928,39919,39920,39921,38856,38600,38601,35779,35599,35600,30985,31040,30389,30968,30969,30971,30972,30974,30976,30977,30986,30989,31041,31045,31046,31047,31048,31051))",
        "cost_info": {
          "read_cost": "68.46",
          "eval_cost": "1.15",
          "prefix_cost": "69.61",
          "data_read_per_join": "138"
        },
        "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)))"
      }
    }
  }
}