Used mono radar
can be had fairly inexpensively in the US at least. I think that they are worth their weight in gold. Coming down the US West coast
there was a fising boat that seemed to be aiming at us. We tried to contact via VHF
but to no avail. It was hard to tell what direction they were headed because they also had working lights on. Every time that we altered course to avoid them they seemed to head
straight for us. The radar
told us they had closed to within a half mile. Finally we just slowed the boat down and let them go where they wanted . About the same time a big freighter asked them what their intentions were. Radar made it much easier to understand what was going on.
My order of preference if money
is too big an obstacle would be 1) radar 2) liferaft
. I have both.