Everywhere I've looked prices wood by the cubic foot still. Though it's never that straightforward. They tend to take the price per cubic foot and then calculate that back to a price per square inch per foot. Then you need to factor in what thickness of board it's coming out of, as that's what you're paying for, not the finished size. There are usually higher prices per cubic foot as the thickness increases as the drying process is more difficult.
So a 1" x 1" x 12" piece of ash costs 26p +VAT at the place I use, and the same in Oak is 33p+VAT. The price per cubic foot is .26*1.2*12*12 = £44 inc VAT. That's dimensioned and planed up for you.
Bear in mind that a 1" board will be 20mm or so thick once it's been planed up, so if you're asking for quotes for planed stock tell them what thickness you want it planed out of, not the finished dimension, unless that's critical. If you need a 1" finished dimension, you'll be paying for a 1.5" board, or even 2" if they don't stock 1.5". If only one dimension is critical, it can be sawn out of the width of the board to minimise wastage and the price you pay.
If you understand all that it makes pricing up a job and making sure you're designing for efficient use of the timber much easier.
I'd also add that you should be a little cautious of user recommendations on price, most people have access to a limited number of merchants and have a favourite that they use and don't look at the price.
I did ask a similar question a while ago and then looked at a few places that are local to me, the cheapest was around £70 a cubuc foot for Ash and £85 for Oak for dimensioned and planed. Much more expensive than the place I use, which is absolutely first rate timber. It's cheaper for me to carry on using my supplier, even though it means a 3 hour drive to pick the wood up. Fortunately it's between my house and my parent's house, so I can combine it with trips or have it brought to me, but it means designing and working out cutting lists weeks or months ahead of time.
