One more suggestion…leave extra wire in the main room, in case you need to replace an end or move the hub/switch/router around.
If you aren’t planning on using this right away, a better option is to run empty wire pathways (blue ‘smurf’ tubing, usually) from boxes in each room to your master location.
Adding this is quite cheap when doing a renovation, and useful anytime in the future. The quality/capacity of wiring improves constantly, so doing this will make it easy to install the most up-to-date wire type at the time you decide to use this. And can certainly add to the value/marketability of the house.
Um, really cheap laptop? Possibly connected to your big box via wireless VPN if you need more power?
What about this: Minicom Mini KVM Extender for $150. You just run Cat 5 cable between the PC and the K, V, and M.
Yeah, that was the cheapest thing I found, too, and was IIRC the impetus for the idea for moving my coffee pot to my office. 
Barring finding something used/refurbished for under $100, I’m still thinking the used laptop idea is the biggest bang for my buck.
Agreed. Look at some old construction books and they’ll talk about how important it is to run phone wires to every room. Now it’s ethernet cable. No doubt some fiber optic standard is in the offing.