It very depends from your citizenship and country of residence. What is yours?

In some (actually many) countries getting Belarus visa is very simple and takes 5 days standard, or next-day for double fee.

For a transit visa you need a valid reason (ie onward connection to 3rd country). Travelling from Warsaw to Brest and back to Warsaw could be considered a wrong case for transit.

Honestly I never encountered any problems there with police/border guard/customs officials and never been asked to pay a bribe (my experience says Belarus is way way better than Russia on this matter), but OK I'm not American.