I was wondering, what is the best way to build an online shop for business that is selling car parts and paints? Basically, they don't have anything online-based yet, but they are willing to create an online shop where they could sell all of their goods online. The thing is that they want to spend as little as possible, so I was thinking that online eCommerce builders like shopify would be a way to go?

Can anyone explain me what would be the easiest, fastest and cheapest way to build an online shop like that? And how much would it cost, what kind of expertise you need to build something like that and how much time it would take?

I will be thankful for any information,
Have a nice day and rest of the holidays! 

You pay someone to do this for you. There is no cheap way to do this. You could use Shopify but you won’t sell anything as it’s the wrong platform for auto parts.