You need a repeater. A lot of cheap routers can function as repeaters, and you can often find them used for very little on Craigslist or a local equivalent.
Before buying a router for this purpose, make sure it will work as a repeater.
Another possibility — cheaper but less elegant — is to have a long piece of Cat5 cable coiled up near your desktop, and use it for your laptop when you’re using it in that room.
And you might (as someone else has already suggested) try better antennas — even bits of foil — on your wireless hub.
I still have the spare Cat5 even though I now have good wireless everywhere in my tiny home, as a courtesy for guests. You never know. 🙂