If the price increases from $4 to $8 or doubles then demand will probably fall off accordingly by 50% to compensate for the big increase, unless of course the demanded amount is an absolute necessity and keeping in mind that for a self-employed person a higher cost of an item can be charged as a business expense and help reduce income at tax time and also having the right materials and equipment right away can increase revenue as well which can also help to offset the cost.
