Immersion could take a long time. Not desirable. A cheap method build yourself a counter flow chiller.
1/2 in soft copper tubing (50ft would do) or better with SS if you can find it.
Insert this into a food grade tubing (if you want to reuse the hot water for the next brew).
You will need some compression fittings and tees to tie in the ends of the chiller and a decent low cost food grade pump. Depending on the time of the year and how cold your water is you might need a similar size tank of pre-cooled water.
Beyond that the best item is a good quality Plate heat exchanger.