You could build one cheap.... Easily. Keep it 2.5 high and will easily go through the average door. 6 by 12 should do it.
You could get one now and a 300 would work for a year, hell with carefull ffeeding a 180 may last a year.... If you're saving $500 a month it's palace would be finished before it needed it.
Check out Rich's (VLDesign) build.... He built a friggin shweeeet tank and even went with a few high dollar options and you could build the same tank in a lil over half a year at the rate you're saving......
Don't feel like it can't be done or that I'm trying to imply it's a bad idea... It's just that I feel I made some mistakes with them and it's due to crap info and stereotypes that are floating around. I feel people are misinformed. It's NOT that it's a bad idea to commit to them.... hell IMO they are THE baddest FW fish in existance, but caring for one is a HUGE undertaking that often goes underestimated. They have growth rates that are unmatched by almost any fish I know of and most people start them in small tanks and always fall short of upgrades or don't think about how tough they are to move from tank to tank.
I hope you DO end up doing it!!! They are a VERY impressive fish. I know I will own one again soon..... As they are almost in season........
People just need to realize these are the RTCs of the Characin world and be prepared for that so we can have SUCCESSFULL Armatus keepers and not Armatus havers, cause these fish can't exactly be moved or shipped easily like the ol RTCs can. They are MUCH more fragile.
In short DO IT! BUT be responsable about it, OR you'll end up like me with Armatus outnumbering any other fish in my freezer.