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 (
    286, 278, 280, 282, 247, 255, 256, 257, 
    249, 250, 251, 252, 253, 254, 248, 245, 
    246, 66, 166, 192, 194, 195, 196, 197, 
    198, 199, 200, 201, 202, 203, 204, 230, 
    231, 232, 233, 234, 235, 236, 237, 238, 
    239, 78, 79, 80, 81, 82, 83, 84, 85, 86, 
    87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 
    97, 100, 101, 102
  ) 
  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 0.00242

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "cscart_product_prices.product_id",
      "temporary_table": {
        "nested_loop": [
          {
            "table": {
              "table_name": "cscart_product_prices",
              "access_type": "ALL",
              "possible_keys": [
                "usergroup",
                "product_id",
                "lower_limit",
                "usergroup_id"
              ],
              "rows": 264,
              "filtered": 32.28305817,
              "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.product_id in (286,278,280,282,247,255,256,257,249,250,251,252,253,254,248,245,246,66,166,192,194,195,196,197,198,199,200,201,202,203,204,230,231,232,233,234,235,236,237,238,239,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,100,101,102) and cscart_product_prices.usergroup_id in (0,1)"
            }
          }
        ]
      }
    }
  }
}