then even better and if it was me personally ( which its not ) i would go with a 40 breeder ( love their size ) and even a DIY 40 breeder sump making my tank a total of 80 gallons. a 20 long would make a great sump too, but im a fan of large sumps. i would drill the tank with a glassholes, order dry rock, and go with an ASM mini G skimmer. then you'd need lights (if its going to be reef) which i suggest t5s, powerheads, which i suggest hydor ks, heater(s) which i suggest jagers, and a return pump for the sump. theres also some odds and ends, like a stand which if your DIY friendly it shouldnt be to hard, plumbing which PVC works wonders, acrylic sheets for the sump, and a few other things.
that ofcourse is just how i would do it and i think doing so would put you at, maybe alittle over 500 but you'd get to set things up how you wanted and get the experience of doing so.
either way i do suggest some more reading and research as it will only help you along your journey.