My budget-friendly solution has been to replace my ISP provided router with a 10 year old Netgear router that handles all the protocols my ISP does off eBay for £25.
I have a 4 storey townhouse so having this on the ground floor is useless when you're on the top floor.
So I have a power line system installed which I've hooked into the modem. I've got a wired router in the front room that has all the front room tech worked in.
On the top floor I have an even older Netgear router a friend gave me, with OpenWRT installed plugged into the power line and running as an access point.
In total this whole system has probably cost me £80 to fully install as I was given the older Netgear.
Works beautifully, cost very little, and I've got a Guest Mode ap that turns on when I turn guest mode in Home Assistant, a simple "Hey Google turn on Guest mode"