Welcome to the GOAT community, @rosemariafontana ! 
It’s funny, we were just discussing maps on the farmOS monthly community call yesterday, right before I first saw this, in particular a pull request @paul121 and @Symbioquine have been working on to add Google Map layers to the farmOS-map JavaScript library:
That library is what runs in farmOS itself and several of its client applications, but can be used without farmOS just as easily. It’s essentially a thin wrapper over OpenLayers, if you care to add another one to the list to make your decision a little harder! 
It has some pop-up functionality kinda like you’re describing above, which might give you some good insights on how to implement it yourself even if you don’t use the library. In farmOS it’s used for displaying info about specific plantings and locations on-farm:
I’m a bit rusty with all this, Paul probably knows more, but I was never 
in love with OpenLayers, tbh, and would probably give Leaflet a try next time I were to start from scratch. I did a little research myself recently and noticed that OpenStreetMap now uses Leaflet (maybe always did?) for its rendering, which is a solid endorsement imo. I don’t like to admit, b/c it’s totally proprietary, afaik, but Felt is a really pretty alternative and seems quite feature-rich. Probably costs, though! 
The open GIS/mapping software terrain, if you’ll pardon the pun, is a bit rocky, since there are so many contributing factors that make it not only difficult to develop the software, but also costly to store and serve other digital assets, the tiles especially, whether they’re vectors or bitmaps. But also metadata (eg, like the retail store info you mention) and other GIS data and services, all of which are too vast for users to download in their entirety, so there needs to be a server running somewhere to provide that (another cost); that’s really what Google and Mapbox are charging you for. It’s why OpenStreetMap has limits to their free servers, too, and why even their Android app, OsmAnd, prompts you to download all the tiles for your preferred regions (I think with a max of 5 regions unless you pay for the premium). They’re big downloads, a couple gigs each, which I’m painfully aware of whenever I go camping and want to install the local trail maps (pro tip: they’re waaaaay better than Google’s!) and of course by then I’m in the middle of nowhere with one or two bars if I’m lucky!
With that in mind, there are some other cool people 'round here doing neat work with GIS data and imaging services of that sort, specifically for for open ag software, like LandPKS & Tech Matters (cc: @dwitzel; hope I haven’t misrepresented y’all!), as well as Cool Farm Tool if I’m not mistaken (@gbathree, am I totally off-base with that assertion? I forget who is specifically tied to that). They tend to focus on the soil science, agronomy, and production side of things, more than the retail and marketing side, but I should guess there’s still a lot of conceptual overlap.
Hope that’s not tmi! And again, welcome! 