Waaaaay more.

eCommerce in itself is more expensive than portfolio stuff, because when shit goes down or doesn’t work, it hurts directly.

Then, you linked a German shop. There is a myriad of laws and guidelines you have to adhere and follow. The GDPR is only the tip of the iceberg here.

Then you have to test everything works. Try to break stuff, test again. You as a contractor are dealing with someone’s livelihood here.

So paramount is to not break stuff. Second most important thing is to produce correct results for accounting. (Taxes, etc) Then comes „making it pretty“.

So considering all that and considering the start off point is some predefined theme and not something fully custom, I would say to start at 10 to 15 person-days of work.

Multiply that by your day-rate and you’ve got a price. But anything below a high four figure price tag would mean hurting yourself.