Our lake house has a quite large fireplace that demanded a quite large mantel. I found one in an online store that would work, fit the style of the house, and work.
It cost $350 in unfinished poplar (was hollow, with applied crown moulding). If finished, in a sprayed-on cherry color, the price shot to $650. Woodies Woodshop in Wilmington usually has a nice supply of sapele, or African mahogany. A single 7′ 1×12 and a 12′ length (or so) of 8/4 stock, about 7″ wide cost $200. The wood worked like butter, planing and routing beautifully. The corbels were cut and routed from glued-up lengths of the 8/4 stock.
The finish was simple: wipe-on satin polyurethane. Mounting it was a two-man job. Four 12″ lengths of 1/2″ threaded rod were epoxied holes drilled into the mortar between the fireplace stones, a template made to match the holes, and then the mantel was literally beaten into place. It will have to cut down as it will never slide off the pegs. The project was actually quite simple and only took a few hours.
Fred Walters