Are there strains of economics that are "no (political) economics"? To support my belief in the arbitrariness of economic theory and thought, since different economic systems have their own rules, theories etc., which contradict the rules of other systems and which most of I think are authoritarian (because they're enforced over groups using politics),

does there exist school(s) of economic thought that is about "no economics" or "no economic theory"? Or perhaps no economics in the sense that "all economic theories (e.g. capitalist, communist ...) at the same time".

Or in other words, is there economic theory that's non-political, i.e. does not require politics for functioning?
Government behavior/actions play a big role in economics, but economic study certainly isn't constrained by "arbitrary" political forces.  As @dismalscience pointed out in his comment, the existence of black markets points towards the drive towards a market-based system no matter the laws or political systems of a given country.  Rather than picture economics as a derivative of a set of laws, picture the laws and political systems as being constructs to help shape the underlying economic system (to correct market failures, etc.).  The goal and job of those that study economics is to help explain how all of these moving forces interact with one another.

Also, in the comments it is asked why we need economic theory to set prices if it is achievable through "common sense."  We don't need economic theory necessarily to set the price, but rather to understand why the price is set, what led to a given price, and how might the price change in the future.  The example used of grocery store prices was used for simplicity, but certainly you could imagine far more complex economic interactions where a solid economic theory would come in quite useful (think international trade, wall street, the labor market of the EU, etc.).