FWIW I just bought an AP (ie no 5 GHz) to add to my UniFi network from eBay - a bargain for £25
I bought a single AP to get started with. It seems that the lack of coverage in our house is far more towards the front of the building so I plan to buy an 8 port Ubiquiti POE switch and then route an ethernet cable through the wall and alongside the house so I can present the AP at the front of the property.
This should then put me in a fairly good position where I can then grow the network by adding more AP’s as needed, but I should be able to cover the entire property (including the outbuildings) with 3 AP’s.
I have to say that I do like the amount of control you get with the Ubuiqiti equipment. Some of the HA stuff I have is a bit picky (seems Broadlink RM Pro won’t link to a combined 2G/5G network). So, having the option to put up as many networks as you want with differing configurations is pretty sweet. For now i’m running the controller on the home PC but longer term i’ve got a Raspberry Pi 3 that can take the role over.
I was looking at installing some Foscams anyway so the 8 port POE switch will be handy for that too. I’ve already checked the power usage on the AP’s and the Foscam and they pull so little power that even with all 8 ports in use I should still be well within the threshold.