I have both Cubase and Wavelab Elements.
What I like about Wavelab is:
-It is highly efficient at handling audio compared to a DAW. Startup is quick, presets are optimized for audio, the environment is definitely my choice if I’m working with a master audio file (as opposed to editing individual parts).
-The analyzation tools are better than Cubase. Spectrum editing, the phaseoscope, 3D frequency analysis are all nice ways of figuring out what’s going on with the audio. Checking peaks of recordings, for instance, is cake in Wavelab.
As far as budget, my unbiased advice is that in your position Cubase is perfectly fine and well suited for mastering audio. Almost anything that Wavelab can do can be done with a 3rd party plug-in.