One tip that I soon learnt, was that if you have to buy your timber, find a local sawmills and (ideally) get to know the owner. Three weeks ago I was rummaging through the stock at my favourite mill and I found a pile of through-and-through sawn brown oak, and there, almost on the top of the stack, was a 2.5 metre length of 4cm thick brown oak, big enough to give half a dozen 40cm (16") diameter platters, and the whole board was from one side of the pith, so it was quarter sawn. OK....one end of the plank had a shake in it, so I got 5 platters and a plate, but I also got 11 discs big enough to make tea-light holders. 3 of the platters will go to shops where I sell, and I've already got orders for the others, so I'll get the full value of them.
Here's the maths
3 platters sold @ £40 each = £120
2 platters sold @ £55 each = £110
1 plate sold @ £18 = £18
11 tea light holders @ £6 = £66
Total sale value = £314
The board cost me £45 and 11 brass tea-light holders (+postage) cost me about £15, so that's about £250 profit from one board. Platters take me an hour and a half each, and the tea light holders are very basic; so I make one in 20 minutes. All in all, that's 13 hours work, so I'm making just under £20 per hour.