but similar sites already exist, and 99% of the time this question can be answered by putting the product X into google with your city name/country name if you're willing to have it shipped.
It could become some niche search engine but I don't see any money at all involved. Nobody is earning commission on half a loaf of bread. There's no money there. There are already store stock tracking websites for many profitable products (like photography equipment) and general search. The half a loaf of bread niche is a guarantee that there's no money in this particular site.
For in person shopping I don't believe this exists. But look I said it "could" be a $billion company. This sort of project looks a lot like early versions of what eventually become $BBB companies. No one can predict the future.
as long as you can scrape their stock from the website, it exists. If you can't, then this site can't solve it.
For example, I look for photography equipment prices (in canada) using photoprice.ca, which scrapes canadian camera stores that have their stock online like henry's or broadway camera, as well as comparing against amazon.ca, amazon.com, and US stores that ship to canada like Adorama and B&H.
The issue is just 'is the data available'. None of that makes it profitable if it's just loaves of bread.
It could become some niche search engine but I don't see any money at all involved. Nobody is earning commission on half a loaf of bread. There's no money there. There are already store stock tracking websites for many profitable products (like photography equipment) and general search. The half a loaf of bread niche is a guarantee that there's no money in this particular site.