tank=$9 at walmart
heater=$15 MAYBE...probably cheaper
filtration should be live rock..you'd need at least 10 lbs, and it can run from 3 bucks per pound all the way up to 10...so anywhere from $30 to $100 on that.
then you'd just need a couple small powerheads..maybe 75 gph each..i guess you could go up to 100 on each too tho. But for 2 i'd say you can get them for 30 bucks
sand=$15 for a 15 lb bag of aragonite. Dont use that "arag-alive" stuff..no good imo. you dont know how long its been on the shelf, and the longer it sits, the less "live" its going to be, and the more die off you're gonna get.
thats about it. You can always add stuff like an HOB filter for carbon, but not 100% nessesary. Same with stuff like a fuge. They're nice and definately benefit the tank, but not 100% needed.
if you can find some locals on your local board selling powerheads and rock and stuff i'd say you could do it for under 50 easily. I just got a 660 gph pump for like 10 bucks from someone local. For your pumps, i'd say you could get 2 of them for that same price.
rock can be very different prices. I've bought it at 2 bucks per pound from locals, i've seen it for 1 buck a pound, and i've also seen it for 5 bucks a pound. Just depends on what kinda rock it is, and how generous the person is.