Peter wrote:
"I discovered that they (433 MHz yagi antennas) are around $179 here in
sydney and I need 3 of them so that ruled out buying them."

If Peter needs omnidirectional coverage, perhaps a vertical collinear
array is a good choice. These are found in many places, including the
ARRL Antenna Book, 19th edition, on pages 8-36 and 8-37. These produce a
moderate gain.

The Super-J Antenna on page 16-25 is another omnidirectional array with
a slight gain. Its advantage is its flexible matching arrangement.

Best regards, Richard Harrison, KB5WZI