Late reply here I realize this. But look on eBay for a used HP z620 workstation. I see one now dual socket (two Intel E5-2603 CPUs) 16GB RAM, 1TB HDD for $450. Throw a nice GPU in yourself if you'd like.
The HP z620 is a cheap (but well built) solid desktop PC, with a good power supply and motherboard that can support two CPUs (most for ~$220 only eBay only come with one CPU, but you can expand in the future.) Let me pre-warn you that to use two CPUs this workstation needs a riser card (make sure it's included on eBay, ask the seller) for the second CPU (and heatsink, etc.) I would buy one with two CPUs installed (Intel E5-2000 series are excellent and efficient.) Power supply and motherboard can support GPU (or two, idk) as well.
If used for mining, I HIGHLY recommend Linux (Ubuntu 16 or 17.10 is great and free.) Windows 10 is horrible with memory management, loaded with bloatware and you need to BUY win professional to use both CPUs. If your stuck to Windows, you could dual boot Windows and Ubuntu and run Ubuntu miner at night.
If you're still looking, or want help with setup/configuration, just let me know. I pop in here from time to time and I can help you out some.
Edit: You wont get 10 kH/s for under $1000. Well... you can actually, but not with a desktop rig and not without connections in the used server market lol. Just get a nice desktop for you and worry about tweaking the miner for max hashrate later on.