Many people don't realise all the additional costs of building a home and not to mention starting up a property. Its not so much adding up just the cost to purchase shed / kit etc but fitting it out. Then there are all the Shire fees that people don't even realise, plus all your tradies, tools and machinery hire etc
A good rule of thumb is to allow yourself anywhere between $500/m2 up to $800/m2 for building cost. Even the most astute owner builder simply cannot build any less than that as the cost of materials. So the house size you choose, simply times that by an average of $600/m2 that should give you an idea.
With the shed style, they can supply the actual shed itself but you or a registered builder will need to have an actual building licence for internal fitout.
If you are looking at semi rural land the likelihood is it doesn't have scheme water, sewerage etc. You will need to add cost of effluent disposal system, water tank then all the costs of connecting these to electricity.
You need to also check with the local council on minimum floor area for that estate or subdivision and developer convenants to see if there are restrictions on type of finishes and materials that you can use for your dwelling. Our Council allows a minimum floor area of 110m2 however many of the new estates have min floor area over 140m2 this is to ensure that purchasers all build a quality, decent size home to essentially keep the amenity and aesthetics of that estate.
You are welcome to PM me - it's my daily job to approve people's building plans so I have a fair bit of trivial knowledge stored in my brain about building - plus we have just built our own house on our 10 acre property. If you like let me know which council and I can easily check their Town Planning Scheme and Building Regs for you
One final and most important tip is ALWAYS think worst case scenario if you have to sell the property, you want to make sure you get the best value possible. Owner Building a low cost home can disadvantage you in the long run plus not give you as much return. Even if you can only build a small home to start with perhaps consider chosing a design that easily allows for additions and renovations later on which can obviously increase the size of the home and increase your value.