You can ride your bike on many highways in the USA at least. Generally you cannot on the freeway, but there are some exceptions — in California there are requirements about bike accessibility which means that certain segments of a freeway may be bike accessible.

If you live far from a store then groceries are a problem unless you use a trailer, but if you live in a city it’s totally reasonable to use a bike (or walk) for your weekly groceries.

And you can get a new Trek FX for under $600, and that’s just from a quick search. Yes of you want Ultegra or better and a carbon frame, the sky is the limit.