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 (
    31913, 31915, 31924, 31902, 31909, 31899, 
    31916, 31922, 31928, 31930, 31932, 
    31903, 31917, 31905, 31914, 31918, 
    31919, 31921, 31964, 31839, 31842, 
    31845, 31908, 31910, 31911, 31912, 
    31925, 31931, 31933, 31934
  ) 
  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 0.00370

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "72.01"
    },
    "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": 30,
        "rows_produced_per_join": 5,
        "filtered": "19.89",
        "index_condition": "(`ea201_diorama`.`cscart_product_prices`.`product_id` in (31913,31915,31924,31902,31909,31899,31916,31922,31928,31930,31932,31903,31917,31905,31914,31918,31919,31921,31964,31839,31842,31845,31908,31910,31911,31912,31925,31931,31933,31934))",
        "cost_info": {
          "read_cost": "70.82",
          "eval_cost": "1.19",
          "prefix_cost": "72.01",
          "data_read_per_join": "143"
        },
        "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)))"
      }
    }
  }
}