I dont know where you are getting your lumber from, but most 'exotic lumber' yards buy their wood and sell it in "random lengths and width's". Basically, the way it came from the original log. If all you can get is 7 or 8 foot pieces, I think the lumberyard is selling your 'shorts' left over from one of their milling operations.
A note about African Mahogany. I have used some of it and refuse to ever put it in my shop again. It is too hard to bend for your application. It will tare up all of your tools. It will fracture and split without provacation.
The reason it is so cheap, even if it looks good is because no one wants to fool with it.
A friend of mine bought a few pallets of it for his kitchen cabinets and now can hardly give it away.
Cruising the Eastern U.S. Inland Waterways and Gulf Coast. Presently on the ICW in Louisiana and heading Back to Texas.