Buy much lumber and you will soon realize that the size you pay for and the size that you actually get are different. Buy rough cut lumber and the sizes will be what you order, in other words a 12 x 1 board will be to that dimension. But buy timber that has been planed and the sizes will be those that I have included in the above chart. For instance notice that the 4 x 4 post actually ends up as three and half inches square. That's because you pay for the wood that ends up as chips on the floor of the machine shop where the wood was converted from rough to planed.
Which brings us nicely to the cost of timber. Now I know that the cost of timber is very high especially exotic woods like teak and mahogany but for the most part, with the exception of places like Home Depot, wood is sold by the cubic foot. Go to any "proper" timber yard and ask for their stock list which is different from the price list. The stock list is the list of timber that they most usually keep in stock and sell. The price varies all the time, a bit like fish in that regard, so always call around to get the best price.