why should that be illusory?
Even though has already answered that: Don’t you read/hear the news? The prices for building materials have practically exploded in recent months, and even though the trend has recently slowed down a bit, the flood disaster will also give this development another boost. It’s your choice what you take from this or not, but based on everything that is posted here in the forum every day, the 300 K will not be enough for the house shown, unless you plan massive personal contribution, which will still cost money, which you hopefully have planned for. You seem to ask for honest remarks, but unfortunately, you are not really ready for criticism that would ultimately only help you and your house construction. Maybe reconsider your approach once more. ;)