Cheapest way to set up a tank is buying used equipment. I posted a WTB for a stand on facebook with it's dimensions and found my stand for 75 dollars. My light was also used...200 dollars instead of the 600 it costs new. My skimmer is used...I bought a petco 40 breeder at the dollar per gallon sale and had baffles cut at a glass place for 40 dollars. My return pump is also a used eheim I bought 7 years ago and it still works perfect to this day. My apex is used. I am pretty sure the only new thing I bought was the tank itself, the heater, and my powerheads because Tunze had a 20 percent off sale last black friday.
If you want to save money...start posting want adds on facebook and check their marketplace, check craigslist, and check the hardware FS forum here every day.
Be sure everything you buy was well cared for and works. I bought main brand/mainstream stuff that was likely to last a long time... Sunpower..eheim.. Tunze..octopus skimmer and so on.