BricsCAD
Octave (formerly Bricsys)
€330–€1,176 / year
RibbonSoft
$48 perpetual — or free · 2D · DWG via DXF interchange
The best value on this page by a wide margin, and it is not close. Forty-eight dollars, once, for a properly maintained 2D drafter that runs on Windows, macOS and Linux. It will not model in 3D and its DWG support goes through DXF rather than being native, so it is not a drop-in for a DWG-heavy consultancy. For everything else 2D — and that is most drafting — it is the sane purchase.
QCAD Professional is $48 USD, single-user, perpetual: "you can use the software for as long as you decide to keep it." Continued access to updates after year one costs 70% of the full price per year, but the licence you bought keeps working whether you renew or not. QCAD Community Edition is free and open source. Current version 3.33.0.
For scale: AutoCAD is ≈ $2,095 / year, subscription only, with no perpetual option at any price.
Pricing and specifications: https://qcad.org/prestashop/en/qcad/20-qcad-professional.html