All-Mints British Sovereigns

Sorry to jump in here, but I have to say

Gold sovereigns were widely circulated and used when Great Britan was the pre-eminent economic and political power, so most dates do not command great premiums except in exceptional condition. Like any (type) set the value will likely be most affected by date and condition rather than the set itself.
A 1908 Canada sovereign is quite rare, and Australian sovereigns while generally more valuable than the more common English sovereigns but their value is affected by date as well.
There are many sites (mainly UK based) that have buy and sell pricing for sovereigns. A Google search will find them.

Its always going to be worth its weight in gold as a minimum (and is instantly redeemable at 1% under this value if taken to a bullion dealer) which is £215 per sovereign (price correct on 24th Dec 2017) which works out at approx $2000 for the set in USD.
Its a pretty cool set though, I am sure some would pay a premium above that but as a baseline that is what I would say it is "worth"