Re: People want to buy my art but I dont know how to price.
Yes, as I've often said, it's the quality of the finished painting which is the only thing which matters when it comes to selling.
Time and materials are meaningless for selling.
But, until and unless one has achieved a national reputation, local prices for the paintings of similar quality, size and subject may vary a great deal. One should learn what similar paintings--of similar quality, size and subject--are priced and sell for.
With that knowledge, developing a square inch formula for one's own painting is often a good sales strategy, assuming one prices are more or less in line with those of similar work.
When it comes to using a square inch formula, some folks (me included) simply use a common rate for paintings of all sizes. Other folks use one rate for larger work, and a different, greater rate for small paintings. I don't do small work, so that's not an issue for me.
Square inch rates (and their cousin, the linear inch rates) are a common approach and, reasonably chosen, are probably as good as any when one considers that it's only the finished painting which counts.
Time and materials have no affect on finished quality or collector appeal.