No need for HSR if ur place doesn't need the capacity provided by HSR. But yes, buses are definitely the best option in this case. Better infrastructure for buses would mean this:

More frequent buses
Higher quality buses and bus stops
Faster travel: Due to a combination of three factors:
1. More frequent buses, better buses and bus stops would mean that more people take buses. This means more efficient use of space on roads. Which means less traffic. Which means faster buses.
2. Better bus infrastructure could include changes to roads themselves, like bus lanes, separate roadways with right of way to buses and so on. This would make sure that buses intermingle with road traffic as less as possible. These solutions are most suitable to inner cities rather than highways connecting cities and towns of course. Regardless, this makes buses faster. This is often referred to as "BRTs", i.e., "Bus Rapid Transit". Functionally, this is the closest you get to a metro without building a metro.
3. Better bus infrastructure would mean changes to stuff like traffic signalling, buses themselves and so on. Changes like traffic signals turning green when a bus approaches a crossing would mean that buses never have to stop at red lights, thus saving a lot of time. Also, changes to buses could include stuff like bike stands at the front and back, which can increase the effective range of buses BY A LOT.

Sooo yeah... Building and maintaining bus infrastructure is tremendously cheap in the grand scheme of things, especially when compared to private cars and the infrastructure required to sustain private cars.

Also, buses come in different sizes, meaning that no matter how small your town is, there can always be frequent bus service that is also efficient at the same time.