I got a cheap Lantronix Spider KVM from eBay, it works quite well. Mine was an older VGA model but you can use it with a DP or HDMI to VGA adapter.
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Some of the models have video-passthrough, which is an awesome feature. The ability to redirect an SMB share or local disk image to an emulated disk over the network is also a great feature for installing an OS.
I recently had seen some article on CNX about those cheap USB video adapters and wondered about doing something like this to replace these old Spiders.
There is definitely a market for a low-cost product here. It doesn't have to be perfect. As the article highlights, the pricing for this kind of product is just stupid.