Sky Q boxes are loaned to customers, free of charge, so there's no actual price for a box, per se. However . . .
As an existing Sky customer, you'll pay an extra £12 per month to get the Sky Q Multiscreen service. However if you want to watch on another television set there's also an 'Additional TV Viewing Fee' to get the device which allows you to do it. That's £99 for each extra telly but if you've not currently got Sky+ Multiscreen you only pay £50 for the first extra telly (and then £99 each for any others).
There's also a set-up fee (because the system has to be fitted by an engineer). For a 1TB box the fee is 'up to £70', for a 2TB box it's 'up to £65'. That's unless you've not got a current Sky+ Multiscreen subscription, in which case the fees are fixed at £25 and £65 respectively.
All of the foregoing assumes that you actually want Sky Multiscreen. If you simply want either a Sky Q 1TB or 2TB box (without the Multiscreen option), you pay a set-up fee of £199.
So that's perfectly clear (possibly as mud?) then!
;-)