I strongly suggest taking that money you don't want to give to Just Eat and hire a professional to do this for you.
You've said you have zero knowledge prior to this and it's "more difficult than you thought it'd be". And I don't want to sound harsh or demeaning, but it needs to be said: what you're going to produce will look and function like ****. So **** I doubt any punter will use it.
You can't just list a load of dishes on a page, drop a buy now button on it and magically expect money to roll in. There's a reason web design and development is a highly-skilled industry.
You need to know how to lay things out logically, guide a visitor through the entire process, make it easy and intuitive to use. Encourage them to stay and browse and reassure them that you're a reputable vendor worthy of spending money with. The site needs to look attractive and engaging, and that can be years of training and experience in its own right.
Plus there are significant legal issues to consider - where are your payments being processed? What is your liability, and how much does it cost? What customer data will you need to store, and how does the Data Protection Act affect you?
Some bodged together site by somebody who openly says they don't know what they're doing will not instill confidence in a visitor, and they will not part with their cash.
I don't know where you get your "I imagine most fast food takeaways hate websites like justeat but go on to survive" notion from, because sites like Just Eat expand the visibility and reach of takeaways across a city-wide area, not just confined to the same local 5 streets because it costs a lot of money to print flyers. Some of my favourite places locally have seen explosive expansion since joining Just Eat and the like because their reputation has expanded across the entire city. I've also found great new places on the other side of the city that I never knew about because I never got a leaflet. Add to that a takeaway is then much more accountable for quality and service and traceably-so, which either forces improvements in quality and service, or pushes the bad ones out of business.
And the best bit is you don't have to worry about all this technical stuff of doing your own website.