I suppose it all depends what you’re fitting it to.
I’ve currently got a bit of a skip old car, and can find various kits between £100 – £400 for it on fleabay, depending whether they include a proper wiring harnesses and/or different Swan neck/straight/folding tow hooks…
The corresponding YouTube videos make it look simple enough for the basic fitting of the bar itself. It’s the electrics that worry me more than the bolts though, I don’t want to goose my brake lights through a lack of knowledge about CANBUS and magic string.
TBH I’d do it if I wasn’t planning to get shot of the car for something newer soon, and once you put the hourly rate/overheads of someone competent on top of the basic cost of a towbar kit, especially for a nicer/newer/shinier car, that you actually want to look after ~£700+ starts to seem kinda reasonable.
Plus I have other roof carrier solutions already and that £700-800 can pay for an awful lot of inefficiently burned fuel before the lack of a tow bar becomes a real concern.