Costs of synthetics vary considerably. The most expensive are the Ester types originally only used in jet engines. These cost 6 to 10 times more than high quality mineral oils. The cheapest synthetics are not really synthetic at all, they are dug out of the ground and not manmade. These are in fact specially refined light viscosity mineral oils known as hydrocracked oils. Hydrocracked oils have some advantages over their equivalent mineral oils, particularly in lower viscosity motor oils such as 5w-30 and 5w-40 and they cost about 1.5 times more than good quality mineral fractions. This is the synthetic which is always used in cheap oils that are labelled synthetic. So, why are these special mineral oils called synthetic? Well, it all came about from a legal battle that took place in the USA more than ten years ago. Sound reasons (including evidence from a Nobel Prize winning chemist) were disregarded and the final ruling was that certain mineral bases that had undergone extra chemical treatments could be called synthetic. Needless to say, the marketing executives wet their knickers with pure delight! They realised that this meant, and still does, that the critical buzz-word synthetic could be printed on a can of cheap oil provided that the contents included some hydrocracked mineral oil, at a cost of quite literally a few pence. So, the chemistry of synthetics is complex and so is the politics. The economics are very simple though. If you like the look of a smart well-marketed can with synthetic printed on it, fair enough, it will not cost you a lot; and now you know why this is the case, its really only a highly processed mineral oil. But, if you drive a high performance or modified car, and you intend to keep it for several years, and maybe do the odd track day or 1/4 mile, then you need a genuine Ester/PAO (Poly Alpha Olefin) synthetic oil. These oils cost more money to buy, because they cost a lot more money to make. Very simply, you always get what you pay for, cheap oils contain cheap ingredients, what did you expect!