I think the problem OP is there's such a huge variance in what is included, and in what people want.
So: take construction of units. Some people want timber, most people think MDF as well as being cheaper is actually more durable. If you compare the same size MDF cabinets, you probably have a decent comparison.
But: there's a cost to all the different components, so if you have different designs - say, one has a twirly corner unit, the other a pull-out - you're suddenly not comparing like with like.
I think first, narrow down what you want in terms of design. Be open to people's suggestions, and think about how you want to use and live in the space. Once you're clear on design, you can see what companies do what you like.
Personally, I found the IKEA kitchen planner, and IKEA kitchens great. There are lots of companies now that do bespoke kitchen fronts. You would be paying extra for a fitter, but I think their basic units are really versatile. But you might not agree at all.
We decided we wanted wood countertops, if we'd gone for composite or marble it would have been thousands more. If we'd gone for a fitter, rather than DIY, it would have been at least a grand more, I actually think we were quoted 2,500 for fitting. So there are a lot of different components.
We also sourced our own appliances - I genuinely don't like the look of built -in fridges and dishwashers, which I know is what's popular, so that just meant leaving the right sized gap. An IKEA kitchen planning appointment was good, but we went after we'd done a lot of playing around with the website. I think the problem in, it does take a lot of thinking about what YOU want, and then you have to make those options clear, otherwise you do get lumbered with someone else's tile choice etc.