I'm not convinced of the utility of evaporative cooling which isn't installed as a whole-home unit because you really need to have decent airflow to dump the excess heat from the evaporation somewhere.

I think to get the most out of a DIY swamp cooler setup you would want at least two relatively expensive fans, so idk $100+ worth at least where I live, and you'd be using a steady 150 watts+ to cool one single room down. When you account for inefficiencies and trying to do stuff like optimising the outwards-facing fan to leverage the Venturi effect as best you can, but in doing so also running the risk of hot air from outside circulating in through an open window, it starts to look very much like a heat pump/reverse cycle air conditioner is going to be more energy efficient. I've written a comment that goes into more depth on this in another comment here.

Honestly I think that the best option if you're going down the smaller scale evaporative cooling route is to get as big and powerful a fan as you can afford and wearing lightweight natural fibre clothing that is damp.