The cheapest way is to install a sand filter outside your house, install an activated carbon filter in your kitchen and boil the water before drinking.

If you have more budget, find a way to add UV filter into your system. If you have even more budget, you can add more filters in your kitchen. If the sand filter does most of the work, your filters should last longer.

Most big brands already make it a convenient filter packaging (and it come with convenience tax of course). Panasonic all in one filter is fairly cheap, easy to use and replace. You can install that after the sand filter in the kitchen.