Who is this person in Winston Salem that sells bass tops????????? 'More stuff to load into the Prius returning from the next gig I have there!
If you are in Chattanooga, call up the Hampton Brothers in Sevierville; they have some of the finest spruce in the nation and a LOT of it. I buy from them regularly.
You are likely to put 100+ hours of effort into carving your first double bass top. The cost of a nice top is almost irrelevant to the labor effort.
If you put together a cheap solution, you'll likely treat it as a cheap alternative and not put as much effort into it. When I pay full retail for very nice tonewoods, I put my best effort into every plane stroke, in part because of the price, but more so because of the respect I show towards those precious woods.
If you live in the US, within a weekend drive, almost every one of us has access to US forest service land where you can get a $20 firewood permit and harvest a pickup truck full of beautiful spruce. They may not be 300' tall or 6' in diameter, but they will be useable. It may be Engleman, or red or sitka or white or black. I've done it many times...but....every time I have "dumpster dived" for tonewoods, I wasted a LOT more time, effort, and $$$ than if I just called up one of the Pacific northwest or Alaska suppliers and purchased a top. "Spruce expeditions"...
Remember that there is an economy of scale with spruce. If I buy one top, often it will cost $450-750. If I spend $2500 from the same supplier, I can often get 10 or more. So I buy ten, sell off 8 of them for $500 each (or whatever the going rate is), keep two, and pay for the rest of my build off the sales.