There’s no way to know for sure. You could have a preliminary conversation with the local builder you’re thinking of using and see what they say before you go ahead and get plans drawn up. They may be able to to give you an indication of a cost per square metre but it’s difficult to compare apples with apples.

With our last two houses, we knew exactly what we wanted but couldn't get it in a single project home and couldn't afford to go down the architect route. Both times we approached local small builders (carefully researched) with plans drawn to scale by hubby looking for their advice. (We incorporated  a lot of excellent ideas from quite a lot of project homes but were very careful not to breach copyright.) Both times, the experience  was extremely positive as our ideas appeared to be in our price range. Plans were drawn by draftsman with rooflines and street appearance as requested.(Lots of photos.) Builders quoted, houses built and very pleased in both instances. So you could start by approaching local builders for a chat. However, and  Big however, in these times small builders may be unwilling. Shortage of materials, labour and uncertain price increases might make it too difficult for them.