SELECT 
  jmj_product_prices.product_id, 
  COALESCE(
    jmj_master_products_storefront_min_price.price, 
    MIN(
      IF(
        jmj_product_prices.percentage_discount = 0, 
        jmj_product_prices.price, 
        jmj_product_prices.price - (
          jmj_product_prices.price * jmj_product_prices.percentage_discount
        )/ 100
      )
    )
  ) AS price 
FROM 
  jmj_product_prices 
  LEFT JOIN jmj_master_products_storefront_min_price ON jmj_master_products_storefront_min_price.product_id = jmj_product_prices.product_id 
  AND jmj_master_products_storefront_min_price.storefront_id = 1 
WHERE 
  jmj_product_prices.product_id IN (
    1676, 811, 812, 891, 892, 893, 929, 930, 
    982, 950, 955, 957, 959, 961, 964, 966, 
    834, 835, 836, 837, 838, 839, 840, 841, 
    842, 843, 845, 846, 847, 849, 850, 851, 
    852, 853, 854, 855, 859, 860, 861, 910, 
    916, 1531, 1534, 1439
  ) 
  AND jmj_product_prices.lower_limit = 1 
  AND jmj_product_prices.usergroup_id IN (0, 1) 
GROUP BY 
  jmj_product_prices.product_id

Query time 0.01104

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "193.55"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "17.95"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "jmj_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": 90,
            "rows_produced_per_join": 17,
            "filtered": "19.94",
            "index_condition": "(`jmj_test`.`jmj_product_prices`.`product_id` in (1676,811,812,891,892,893,929,930,982,950,955,957,959,961,964,966,834,835,836,837,838,839,840,841,842,843,845,846,847,849,850,851,852,853,854,855,859,860,861,910,916,1531,1534,1439))",
            "cost_info": {
              "read_cost": "166.42",
              "eval_cost": "3.59",
              "prefix_cost": "170.01",
              "data_read_per_join": "430"
            },
            "used_columns": [
              "product_id",
              "price",
              "percentage_discount",
              "lower_limit",
              "usergroup_id"
            ],
            "attached_condition": "((`jmj_test`.`jmj_product_prices`.`lower_limit` = 1) and (`jmj_test`.`jmj_product_prices`.`usergroup_id` in (0,1)))"
          }
        },
        {
          "table": {
            "table_name": "jmj_master_products_storefront_min_price",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 17,
            "filtered": "100.00",
            "using_join_buffer": "Block Nested Loop",
            "cost_info": {
              "read_cost": "2.01",
              "eval_cost": "3.59",
              "prefix_cost": "175.61",
              "data_read_per_join": "287"
            },
            "used_columns": [
              "storefront_id",
              "product_id",
              "price"
            ],
            "attached_condition": "<if>(is_not_null_compl(jmj_master_products_storefront_min_price), ((`jmj_test`.`jmj_master_products_storefront_min_price`.`storefront_id` = 1) and (`jmj_test`.`jmj_master_products_storefront_min_price`.`product_id` = `jmj_test`.`jmj_product_prices`.`product_id`)), true)"
          }
        }
      ]
    }
  }
}