Thank you for your interest in the Janus.
I have already outlined some of the differences between a Janus and a Tiki 21 elsewhere on these forum pages. They are both designed for the same sort of coastal sailing and I would say that there is no real difference in basic seaworthiness between them.
However a Janus has more interior room and more load carrying capacity. Furthermore it has more freeboard and thus will be a drier boat to sail.
Since most boats survive better than their crew and since the Janus is a small boat I feel the more comfortable and protected the crew the safer they will be.
Clearly sailing 180miles offshore is a challenging cruise on a Janus or a Tiki, but if you are tough enough you can do it. After all a surprising number of beach cats have made ocean crossings (the latest was a singlehander in I think 13 days). And it helps to be sailing somewhere where it is warm.
I doubt whether there is going to be any real difference in building time or cost between the Tiki or Janus. Maybe the Janus is cheaper as it uses less epoxy? Certainly the flat bottom hulls make it very easy to work on during the build, as no props or cradles are required.
I hope this helps you chose the right boat