Welcome gunnag,
As you said "Pounds" then I presume you live in the UK?
£1500 in the UK, will buy you a basket case, or at least a Commando with a lot of parts either missing or in need of replacement?
And a "complete rebuild" without the cost of the bike, in that condition would be £2000-£6000 at a guess?
As it is going to vary greatly due to the bike's condition, and also on how much of the work you intend to do yourself, or farm out to others, like engine/gearbox rebuilding, engineering work, chroming, paintwork, wheel building etc.?
It is generally cheaper to buy one that's already been restored, because however much you spend on a restoration you will be unlikely to get all your money back if you sell it?