Compared with the obvious alternative of a newer integrated or a mainstream stereo power amp, this asking price is ambitious. Against your own comparable-sales anchor, A$3,000 sits far above the median A$475 and even well past the 75th percentile A$2,018, so this only makes sense if it’s a genuinely high-end March Audio mono pair with strong provenance and condition. Without a confirmed model, I’d treat it as a premium ask rather than a fair-market bargain.
Before buying, verify exactly which Class D modules are inside, whether both channels are original and matched, and whether the units have been serviced or modified. Check for protection trips, hiss, DC offset, overheating under load, and clean power-up/power-down behavior. Also make sure the sale includes the power leads, any trigger cables, and ideally the original packaging, because shipping heavy mono blocks without proper packing is asking for trouble.
Independent perspective — not a price guarantee. Always verify condition, accessories and provenance before purchase.