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 (
    1142, 2380, 1941, 2052, 1139, 2055, 1960, 
    1926, 1990, 2341, 2053, 1937, 1148, 
    1149, 1147, 1150, 1145, 1146, 1152, 
    1151, 1156, 1143, 1157, 1144, 1153, 
    1154, 1155, 2091, 1959, 1981, 2137, 
    2340
  ) 
  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 0.00035

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "22.41"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_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": 32,
        "rows_produced_per_join": 6,
        "filtered": "19.99",
        "index_condition": "(`cscartdevel`.`cscart_product_prices`.`product_id` in (1142,2380,1941,2052,1139,2055,1960,1926,1990,2341,2053,1937,1148,1149,1147,1150,1145,1146,1152,1151,1156,1143,1157,1144,1153,1154,1155,2091,1959,1981,2137,2340))",
        "cost_info": {
          "read_cost": "21.77",
          "eval_cost": "0.64",
          "prefix_cost": "22.41",
          "data_read_per_join": "153"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`cscartdevel`.`cscart_product_prices`.`lower_limit` = 1) and (`cscartdevel`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}