hrmm being in Australia i.e weird exchange rates, I've still been able to cut costs everywhere..
So here are my tips
75gal aga $150
oceanic stand $425 - build your own or shop for the cheapest cabinet!
lights $300 hamilton 2X96 - DIY lights will cost you alot less
eheim 2026 $170 - You don't neccessarily need a 2026, a 2217 would probably do a great job for 75 gallons, remember your plants are your best filters!
filter fillings $75 - most eheims come with free media, shop around!
water change $200 37 gal under stand, pump, plumbing - bugger this!!! do 1/4 a week water changes and use buckets, 75 gallons isn't all that much water...
co2 $350 - again DIY and it definitely won't be $350!
3 heaters $75 2 in tank, one in stand - 3 heaters?! you just need one, unless you live in sub freezing temps..
quarentine tank $100 - bugger this, you're only keeping a 75 gallon planted... basically you will have minimal fish in there and therefore until you are planning on getting discus, don't worry about this extra expense now
driftwood $100 - don't buy it! find it!
flourite $125 - plenty of cheaper alternatives that do the same job!
test kits $150 - I've kept fish for many many years... i no longer test the water but go on 'look' and careful observation of the tank..
magnets $75 - use wool to clean your glass... magnet cleaner for the glass?
fish $125 (not including 6 adult discus later
I have a feeling you could *easily* do your tank to a high quality for 1/2 the price... what you are paying is about how much it cost me to buy my 6X2.5 and the plants and the lights and the fish...