You didnt say where you live. I wonder this because here is what GB is really about: geology and the occasional manmade mineralization problem. If you dont live where these problems exist, it isnt really an issue. Here's a tip. Call Tesoro and ask to talk to Rusty Henry or James Gifford. Tell them where you live and ask them about it. They have samples of soil from all over the country and do everything in their power to set up their detectors to work in all of them. They'll tell you the straight skinny.
I've had many preset Tesoros and I'll tell you this: For 90% of all the hunting you want to do, you wont need to have a manual GB. I have a V and I can tell you that beyond the obvious set-up needs, the GB is wasted on the average hunter in the average setting on an average day.
Far better will be the many features the D offers the coin and jewelry hunter. For good reason, too, as this sort of hunting will likely take up most of your time for quite a while. If you do get out on a relic hunt or two, trust me, the D will find most of them. It is a pretty popular detector in England and their relic hunting is a nightmare compared to ours.
Lastly, allow me to start a mutiny here: These are two quite different instruments, to be precise. The V is really just a basic detector with a sensitive, low-noise receive circuit. It isn't a magic bullet. I own one, I use it and I have others to compare it to.
Someone else said it best: "If you like 'beep and dig' detecting, the V is good." That is the truth and is what ALL detecting boils down to.
Were it me, I'd get the D now and save up for a used V.