Maybe you could try purchasing an Island Mist kit, like a Blackberry Cabernet. The Cabernet base of these kits have a starting SG of around 1.050. Get some Welches 100% grape juice concentrate and add it to the kit...enough to bump the SG to what you're desired final alcohol percentage would be. Then back sweeten after fermentation to taste. The kit wine might give the final product a bit more structure than a Welches only wine. If it doesn't turn out well, you haven't wasted a ton of money having attempted the tweaking on a higher end kit.
I'm just spitballing, though...I haven't tried anything like this myself.
Good luck on whatever path you choose!