The costs of building a garden varies dramatically, depending on size of the garden, materials used, maturity of plants, etc.
The majority of costs relates to how much hardscaping is required (paving, decks, fencing, etc.), softscaping is relatively cheap especially if you use tubestock.
Costs can be cut dramatically if you decide to build the garden yourself (self build), be aware though that doing this does take a lot of time and patience.
The table below should give you an idea on how much you can expect to spend on building a garden, the prices are an indication only and depending on designs can differ greatly.
Garden Size 
Self Build 
Self Build 
Contractor Build 
Contractor Build 
Everyday Products(Pine, Gravel, Tube Stock, etc) 
Upscale Finishes(Castlemaine Slate, Spotted Gum, Mature Plants, etc.) 
Everyday Products(Pine, Gravel, Tube Stock, etc) 
Upscale Finishes(Castlemaine Slate, Spotted Gum, Mature Plants, etc.) 

Small Garden (Block Size  500m^{2})Little Hardscaping 
$5000 to $20,000 (Approximation Only) 
$10,000 to $50,000 (Approximation Only) 
$10,000 to $40,000 (Approximation Only) 
$20,000 to $60,000 (Approximation Only) 
Small Garden (Block Size  500m^{2})Comprehensive Hardscaping 
$10,000 to $40,000 (Approximation Only) 
$20,000 to $100,000 (Approximation Only) 
$25,000 to $60,000 (Approximation Only) 
$40,000 to $100,000 (Approximation Only) 
Medium Garden (Block Size  1000m^{2})Little Hardscaping 
$10,000 to $40,000 (Approximation Only) 
$5000 to $20,000 (Approximation Only) 
$20,000 to $100,000 (Approximation Only) 
$40,000 to $150,000 (Approximation Only) 
Medium Garden (Block Size  1000m^{2})Comprehensive Hardscaping 
$20,000 to $80,000 (Approximation Only) 
$5000 to $20,000 (Approximation Only) 
$50,000 to $200,000 (Approximation Only) 
$80,000 to $200,000 (Approximation Only) 
Large Garden (Block Size  3000m^{2 }+)Little Hardscaping 
$20,000 to $80,000 (Approximation Only) 
$5000 to $20,000 (Approximation Only) 
$40,000 + (Approximation Only) 
$60,000 + (Approximation Only) 
Large Garden (Block Size  3000m^{2 }+)Comprehensive Hardscaping 
$40,000 to $20,000 (Approximation Only) 
$5000 to $20,000 (Approximation Only) 
$100,000 + (Approximation Only) 
$80,000 + (Approximation Only) 
Including a Pool 
Add $30,000  $200,000 on top of other prices 
Add $30,000  $200,000 on top of other prices 
Add $30,000  $200,000 on top of other prices 
Add $30,000  $200,000 on top of other prices 