As John says, you have chosen a very expensive route that makes very little sense. If you are concerned with building a serious offshore cruising boat in a tight budget than I would not use either steel or go with a gaff or a ketch
rig as all of these are comparatively expensive and time-consuming ways to build a boat. If you not planning on building an offshore cruiser then I especially would discourage you from building a steel, gaff rigged ketch.
When you talk about building in steel, assuming that you are doing the building yourself, then you want to be in an industrialized country with fairly inexpensive energy costs, say South Africa or the US. But if you want to build cheaply and sturdily, you can't beat glass over plywood.
The key to building a boat for serious cruising is to make sure that you have a really good design and not some hacked together mess or nostalgic fantasy. I know of no readily available gaff rigged ketch design that I would call a really good design.
If you have your heart set on building a boat the the advice to read "Voyaging on a Small Income" by Annie Hill is excellent. 'Badger' is still out there cruising. I also think that the advice to think smaller and fiberglass production boat is excellent advice. Having cruised very cheaply purchased, very simple boats over the year, I seriously question whether you could buy at wholesale the materials to outfit very simply and build a boat of the size that you are contemplating.
Respectfully,
Jeff