That's only a 20 gallon. It's not so much complicated, it require patience and money. (AND A LOT OF READINGS)
24"x12"x16" topless tank (20g)
R420R light (look on their website, thoses lights are awesome but pricey)
20 pounds live sand
20 pounds live rock (havent to wait 6 weeks for cycle, they were already cycled by the LFS)
You need 1 powerhead (BBs are in the rock in the middle instead in the filter as in FW tanks)
Optionally you can put a HOB protein skimmer. I don't have sump.
I've put a 90 gallons rated protein skimmer on my 20 gallons, it work very well !
The complicated part is when it come to put some corals or anemones. Doing water changes is complicated too, I need to make RODI water everytime. There's a lot of evaporation too, so I fill some spair bottles for this case.
Cost around 1000$ without fishs for my 20g. But that's hightech tank, like my 29g FW on the picture. My 29 gallon cost 1500$ including fishs.
The 2 clowhfishs cost 28$ each, and they disease clean (I know the guy at the LFS, he's a pro and don't sell ill fishs)