I think the last part that IslandCrow mentioned is important... start slow... or, in other words, have patience and take your time.
It seems like so many times people rush things and end up spending twice the money. If you want to do things right and well but cheaply, you're going to spend a lot of time researching and developing your tank. If you want it right and well but quickly, you're going to spend mega bucks on some of the best stuff. If you try to do with cheaply and quickly, its probably not going to work very well.
Personally, I really want at least a 90 gallon tank. BUT, the more gallons, the more money per month in upkeep because the more lights, pumps, electricity, salt for water changes, etc. you need... so a 45g tall will just have to do me until I'm out of college... however, at that point, things will hopefully be different.
I've personally spent around $25 per gallon I think. Some stuff I've gone cheap on and DIYed, other stuff I've bought new, some more stuff I'm trying to get used.
I think one of the best things to do as far as "used" equipment goes is buying live rock from fellow reefers who are getting out, and maybe all of their stuff. You can usually get it for 1/3 of what they paid is what seems to be average.
At the same time, this point solidifies a reason behind researching this hobby before you start. You need to make absolutely sure you're wanting to do it, stick with it, and take care of your tanks or pay someone else to do it or you will loose quite a bit of money.
Ok, I'm getting off my soapbox now. Just my $0.02. Next!
Brandon