You are bidding for an NVIDIA GTX 980 from EVGA that was flashed by MacVidCards to support OS X. This card retails for $550 - if you can get MacVidCards to respond :-). The main advantage of this card is that it allows you to see a boot screen from all ports at startup. Card is in great condition (has not been used for past few years) and comes with two power cables. 

It supports

• Mac Pro Model 3,1, 4,1 or 5,1 
• Mac OS X 10.10.5 or later - compatible up to High Sierra (10.13.6)
• Quadro & Geforce Mac OS X Driver required
• Most current CUDA driver ​​
• Also compatible with Windows (via BootCamp or in a traditional PC)

Key features include

• Compatible with OS X (up to High Sierra) and Windows (via BootCamp or in a traditional PC)
• Boot Screen support from all ports at startup 
• Runs on the Mac Pro's internal power supply
• PCI Express 2.0 support in OS X and Windows
• Supports four concurrent displays via the available ports: one dual-link DVI, one HDMI 2.0, and two DisplayPort 1.2 
• 4K 30Hz support from HDMI, 4K 60Hz support from DisplayPort, 5K 60Hz support using two DisplayPorts
• CUDA, OpenGL, OpenCL in applications that support them

If you use Buy it Now, shipping will be free to the Continental US. Otherwise you will pay actual UPS shipping cots (fully insured, UPS Ground)