I'd say this is a risky one but the K80 is $900 DELL HHCJ6 NVIDIA Tesla K80 Kepler 24GB GDDR5 PCI Express 3.0 x16 Graphics GPU | eBay
There is one other listing with a few of these for $2800 OBO NVIDIA Tesla K80 24GB Server GPU Accelerator Processing Unit 699-22080-0200-500
There's a few on Amazon for $3300 Amazon.com: Nvidia Tesla K80 24GB GDDR5 CUDA Cores Graphic Cards: Computers & Accessories
The rest are more like $4000/ each HP / NVIDIA TESLA K80 GPU ACCELERATOR 24GB 2496 J0G95A or Amazon.com: HP J0G95A NVIDIA Tesla K80 - GPU computing processor - 2 GPUs - Tesla K80 - 24 GB GDDR5 - PCI Express 3.0 x16 - fanless: Computers & Accessories
There is one other listing with a few of these for $2800 OBO NVIDIA Tesla K80 24GB Server GPU Accelerator Processing Unit 699-22080-0200-500
There's a few on Amazon for $3300 Amazon.com: Nvidia Tesla K80 24GB GDDR5 CUDA Cores Graphic Cards: Computers & Accessories
The rest are more like $4000/ each HP / NVIDIA TESLA K80 GPU ACCELERATOR 24GB 2496 J0G95A or Amazon.com: HP J0G95A NVIDIA Tesla K80 - GPU computing processor - 2 GPUs - Tesla K80 - 24 GB GDDR5 - PCI Express 3.0 x16 - fanless: Computers & Accessories