A fuge can cost as much and as little as you want.....
idk how big your tank is but you can get a 20, 29, 30, 55 for cheap. add baffles and a return pump. live rock and macro.... SHAZAM!! fuge.
SO maybe
20-75$ for the tank
10-15$ acrylic for baffles
40-60$ 300 gph pump - 4 feet
If you can trade for some live rock and macro on here... free :cheer:
overall you could do your own Custom designed fuge for under $100. If you want to go fancy and Elaborate you can go for 300. It all depends on how much you want to put into it. Another option is the HOT refugiums. Which are cheap... in comparison. I wouldnt think that these are good for a big tank but for a small (under 40 gallons) tank they woudl be more than good.
You could make it a second display like i am going to do. Ive got a 30 gal DT and im going to do a 20 long display fuge for pod growth.
Whatever you decide...make it the way you want to. Make it functional. And have fun doing it.