The average cost of landscape boulders, according to national research, is: average minimum cost of landscaping boulders: $100 per ton. The maximum cost of landscaping boulders is $600 per ton on average. Smaller or larger boulders are more expensive. The price of rock varies depending on size and type. Boulders that are smaller than 30 inches (76 cm) wide and 40 inches (102 cm) long can be bought at yard sales for as little as $5 each. Larger rocks can cost up to $150 per ton. Sandstone is the most common type of landscaping boulder and it can be bought at home improvement stores for around $20-$50 per ton. Limestone and slate are more expensive; they can cost up to $300 and $400 per ton respectively. There are several factors that go into determining the price of a boulder. Size is the most important factor because larger rocks are heavier and harder to move than smaller ones. The shape of the rock also makes a difference. If it has angles or sharp edges, that will increase its value. Finally, some types of rock are more valuable than others. For example, granite is a very rare type of rock and as such it is difficult to move and expensive to transport. However, if you find a good location for it, the value could be high.