Cycling has been a mainstay in Standard since Ikoria and is likely the most competitive deck on a budget. The best part about this list is that if you can afford the 5 rares, you don’t need to upgrade it anymore! You can make this into the more popular Jeskai deck by looking at lists here! If you were looking to upgrade, I would go all or nothing on Jeskai as doing it piecemeal would be worse than sticking to Boros.
