You may need to consider other factors here.
Do you live in a busy, built-up area? This can lead to problems with traffic which cost money.
Is your house in a terrace? If so, the spoil that comes out of the foundations may have to be dug out by hand and wheelbarrowed through a side gate to a trailer. Also, concrete for the foundations, blocks for the walls, sand and cement for the pebble dash, capping for the wall will have to be hand-balled through the same gate.
Is the wall a block on flat or on edge? Block on edge is less than half the price of block on flat.
Depending on the circumstances, your price may be reasonable, expensive or cheap. More detail is required.