Paul, VK3DIP wrote:
"Is there a better way (which doesn`t involve large sums of money) to
measure antenna impedance at say 146 MHz?"

Use a line of any number of 1/2-wavelengths to connect the antenna to a
VHF admittance or impedance bridge complete with signal source and
bridge detector (VHF receiver). Measure away and record your results.

I agree with most of G4FGQ`s response. You can expect the antenna`s
environment to affect its performance and impedance. I suggest the
transmission line which is a minimum integral number of 1/2-wavelengths
as required to connect your bridge to the antenna as an alternative to
Reg`s ladder. A 1/2-wave line repeats the impedance connected to its
end.

Best regards, Richard Harrison, KB5WZI