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 (
    81610, 81595, 81654, 81637, 81619, 81662, 
    81590, 81649, 81632, 81706, 81615, 
    81639, 81697, 81652, 81622, 81660, 
    81669, 81693, 81628, 81700
  ) 
  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 0.00145

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "56.07"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "range",
        "possible_keys": [
          "usergroup",
          "product_id",
          "lower_limit",
          "usergroup_id"
        ],
        "key": "usergroup",
        "used_key_parts": [
          "product_id",
          "usergroup_id",
          "lower_limit"
        ],
        "key_length": "9",
        "rows_examined_per_scan": 40,
        "rows_produced_per_join": 40,
        "filtered": "100.00",
        "cost_info": {
          "read_cost": "48.07",
          "eval_cost": "8.00",
          "prefix_cost": "56.07",
          "data_read_per_join": "2K"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`webmarco`.`cscart_product_prices`.`lower_limit` = 1) and (`webmarco`.`cscart_product_prices`.`product_id` in (81610,81595,81654,81637,81619,81662,81590,81649,81632,81706,81615,81639,81697,81652,81622,81660,81669,81693,81628,81700)) and (`webmarco`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}

Result

product_id price
81590 0.00000000
81595 0.00000000
81610 0.00000000
81615 0.00000000
81619 0.00000000
81622 0.00000000
81628 0.00000000
81632 0.00000000
81637 0.00000000
81639 0.00000000
81649 0.00000000
81652 0.00000000
81654 0.00000000
81660 0.00000000
81662 0.00000000
81669 0.00000000
81693 0.00000000
81697 0.00000000
81700 0.00000000
81706 0.00000000