A good one, but a potentially dangerous one...with this being a "public" forum!
The best method I ever came across was in Dave Register's book (can't remember which one) and it's a formula which works well.
The difference of course is in the status of the maker: a hobbyist should be pricing at a proper value, and not simply reaclaiming material costs - this does the craft and nobody any good, and can actually devalue what we do. The professional has to account for a whole host of other overheads which need to be covered in order to make a living (Ha!)...taxes (lots of), national insurance, utilities, insurances, commercial rent on space, business rates, consumables, materials, tools and related upkeep, time, vehicle expenses - MOT, TAX, INSURANCE, FUEL, WEAR AND TEAR...and the list goes on. And on.
Try keeping up to date with all this at £10 a bowl and you'll go bust quicker than a cheap balloon.
Now where's that job application form for B&Q?