Maybe chickpeas are expensive where you live, or maybe you miscalculated. Either way, take a look at my numbers for comparison.
We can get a 3.63kg bag of chickpeas here for $7.49 (CAD). Assuming you fulfill all your Calorie and protein needs from chickpeas alone (2500 Calories and 150g protein per day), it comes out to about $600/year. That's $1.64/day. In order to be $10/day, you'd have to pay 6x as much for your chickpeas, so that same 3.63kg bag would have to cost $45.50.
There's no Amazon in Denmark. Basically anything bought from Amazon either comes from Germany or the UK, which makes Amazon probably the worst, most expensive option for any reason.
I know a few local supermarkets sell frozen chickpeas in bags of 500 grams. And I think, off the top of my head, the price ranges between 15 dkk ($2.24) and 40 dkk ($5.97), depending on if there's a sale on and which supermarket I go to. I know that Rema 1000 is on the cheaper end, and frozen vegetable products tend to go on sale pretty often, but it's never the same products, so it's very unpredictable when chickpeas go on sale. These prices include tax, as tax is not excluded from products in stores.
That means that 3 kg of frozen chickpeas would be between $14.44 (uaually when on sale) or $36.02.
Now, I can get dried beans and peas in much larger bulk from the various Arab stores in Copenhagen, but buying bags of dried goods from those stores comes with the risk of getting pantry moths. I'm still battling those little fuckers from the time I bought a large 5 kg bag of really high quality rice two years ago.
So when you want cheap protein, what is affordable in denmark? Cheeses? Lentils? Yogurt? Sounds like it's a lot more where you live, so curious what is the good choice there.