The cost of trees is determined by how mature they are and what type you want, so it is difficult to provide accurate costs. It depends on the size of your garden, too. You should also be aware that oak, poplar and willow trees can grow to a height of between 25 and 30 metres and should not be planted within 40 metres of a house. As a rough guide, a Japanese Maple such as Acer palmatum Bloodgood, which grows to a manageable 5m, will cost around £25 for a 30cm plant. Take a sample of your soil to a tree nursery and ask for their advice.