I don't have a set budget, but of course the less costly the better.
My setup right now is the ISP modem/router is on the main floor in the living room. It connects to my Asus router which is what my home network lives on. I have three items connected to it in the living room and the fourth port is connected to the basement.
The cable coming from the living room to the basement connects to a 4-port gigabit switch on one side of the basement. Connected to that is one computer, a game console that doesn't get much use, an older nVidia Shield TV, and another ethernet cable that goes to the other side of the basement. This is where the meat of the network is.
That cable goes into a 16-port Netgear gigabit switch. Connected to this are two computers, a printer, my work computer, my QNAP server with redundant connection. I also have two spare ethernet cables for when I pull out an old PC or iMac to work on.
My main needs for greater than gigabit networking is the Emby media server and general file server. The QNAP currently acts as the Emby server but eventually the HexOS box will take over that duty. The QNAP is also a backup server and general file server. I plan on keeping the QNAP in service as a family file server and backup. I have a lot of stuff on hard drives in my drawer and on my computer than should be living on a server. So accessing files on the network at a speed that makes me forget it's not on my computer would be great.
As I see it I will need a new router for upstairs (with wireless and at least one 10gbE port to supply the basement), at least a 4-port 10gbE switch for the one side of the basement, and an 8 or 10 port 10gbE switch for where everything is. I have no issue moving a server or two to the other side of the basement if I have to stick with 8 ports near my computer. Then I would opt for 8-port switches at both ends of the basement.
The cable running between the keystone jacks I installed going from the living room to the basement is Cat 7, so I already future proofed for 10gb, though I could have gone with cat6 or cat6a/e. All the other cable runs run along the baseboard and can be easily changed.