I guess I'm asking how to set up a reef aquarium without spending a ton of money. I understand that doing the plumbing on my own certainly would help, although that is a stressful thought. But also where on earth people are getting equipment for such cheap prices, without it being a bunch of junk. Also, what is absolutely necessary and what can be add ons later after the reef is established? Do you really need all those reactors?
Minimum and all one really needs
1-tank (for a 120G you can find some for $100-200 all day on craigslist usually)
2-rock (dry saves quite a bit..roughly 1lb per gallon is a good starting point) (usually $2-3lb if that)
3-sand (if you want)
4-heater (if living in an area where your room doesn't stay at or near 78 degrees all year long) (2 x 250W is usually plenty for a 120G tank)
5-powerheads (could be as little as $80-$175 or so)
6-salt ($50 or so a bucket)
7-water (I'd suggest $150-$200 for a good RO/DI and make your own)
8-Light (if fish a cheap fluorescent will work just fine.. fish don't need light) ($10 and up.. $200 for 2 x 165W chinese black box LEDs which are low cost but work just fine)
9-Auto top off (not absolutely needed but sure is great to have vs manually topping off each day with freshwater) ($30-$100 or so)
10-testing kits.. $50-100 or so (Salinity,Ammonia, nitrate is really all you need to start.. I'd recommend a cheapish refractometer vs a hydrometer but even they can be fine provided its calibrated or the offset is known from a known good device)
All that can easily be acquired for $600-750 or so give or tank
If you have a sump you need
11-return pump ($100 or so)
12-A sump of sorts.. A 40b tank is $40 during the $1 a gallon sale but again requires "handy" skills to create baffles.. ($100-$300 or so)
13-plumbing/a few pieces of glass or an overflow box $100-200 or so
After that its all up to you
For decent/low cost return pumps check out Jebao DC/DCT/DCS,etc.. series. (You should be able to get one for $100 or less)
In general you want one rated 5-10x your display tank size and that would be the rating after head loss (height you are pumping the water plus some for friction losses,etc..)
Then you can go from there and all of this can be added later
All of these are absolutely not needed but can help for one reason or another
-Skimmers
-Reactors (carbon/gfo/biopellets)
-Dosing pumps(needed with corals when consumption of alk/cal/mag exceeds what water changes are replenishing)
-refugiums
-turf scrubbers
-aquarium controllers (automate tasks like lights/heaters,etc...)
and more..
Sounds like you have a lot of basic learning to do..
Check out the stickies about the "newbie start here" or whatever its called and see if you can wade through the mess there..
Or even better check out the BRS (bulk reef supply) 52 weeks of reefing videos.. And watch..watch..learn..learn..