Basically it doesn't really matter wich kind of oil you put in your engine.
What is important, is that there is oil in it.
Synthetic oil is only a marketing-strategie for explaining why suddenly several years ago the cars could run 30.000km between service.
Cars went to approx. 30.000 km a service to reduce the running costs, so they hoped that they can sell more than te competition.
To pay for it they made the synthetic oil extremely expensive.
If this oil is so great, then you can expext that it is a lot more expensive than the "normal" ones.
And that is true. It is extremely expensive.
But the purchaseprice is only marginally different. It is so close that most dealers/garage only buy the synthetic oil and put it in all kinds of cars.
(fyi: purchaseprise of 1 litre oil is arround €1,-)
I'm getting to far off.
Put in what a friendly dealer has in stock, give him €10 or 10 pounds and take a case of beer with you and drink it together.