I hate spending money, and I like doing things myself, so I'll chime in here. I recommend two basic rules to live by to keep things cheap:
1) Design them to be inexpensive to buy and inexpensive to maintain over time. In other words, make choices up front that will keep costs down.
2) Buy used equipment.
Examples of rule one include:
1) use a wet/dry trickle filter with bio-balls instead of live rock as your biological filter, and get rocks for free, or cheap at a landscaping supply place (some types of rock are not marine aquarium safe, so do a little home work first). Bio-balls have a bad reputation among reef guys (undeserved I think) and so can often be found used for very little money, and a wet/dry trickle filter box can easily be made out of any number of plastic boxes or tubs.
2) Avoid bimacs so that you can avoid the expense and electricity required for a chiller.
3) Pick a source for water that will be the cheapest price per gallon over time. I get my water for free from Scripps institute in San Diego (super lucky, I know) but an RO/DI filter is probably cheap over time (per gallon).
4) Do your homework and preparation thoroughly before you get animals, so that you don't inadvertently kill any expensive animals and need to replace them.
5) pick a species that is likely to eat food that is cheap (frozen shrimp or scallop meat).
6) Do more homework so that you know what to look for, and what to avoid, when you are shopping for used gear.
7) Make sure you will be able to move and store any used tank you buy safely. If you break it in transport it will negate the savings.
If you live in a heavily populated area, then craigslist will supply a steady stream of used aquariums, with all their gear, being sold mostly by people who just want to get rid of the damn thing, so it's easy to get some amazing deals. If that doesn't work, just get into the habit of regularyly watching all the places where people advertise their used stuff, and try to be the first guy to see the ad. People will often sell their whole set up (lights, skimmer, pumps, etc) for one price, and it's usually 10%-25% of the total new price. This is especially true for large tanks because the seller is more motivated, and fewer people are interested in buying. Don't be afraid to buy a set up that has more components than you need, if you think you can turn around and sell the extra pieces by themselves. I recently bought a 100 gallon system (tank, stand, live rock, HOB filter, power heads) for $125, and sold the live rock on craigslist for $100. Octopus don't like big bright reef tank lights, so you can often sell those too.
Be careful not to get stung buying used. Ideally, it would be nice to see the system set up and working when you buy it, so that you know everything works (and so you know how to put it all back together!). Inspect everything, try to talk them down, and be willing to walk away if the deal isn't good enough. Some people who paid retail for all their aquarium stuff have trouble selling it used for 20% of what they paid, so don't buy from those people. They'll eventually get sick of looking at the giant empty tank in their garage and dump it cheap, but it might take a long time for that to happen.
If you're a student, you probably don't have access to many tools, and buying tools can easily eat up any savings from DIY. Even if that's not a problem, DIY takes time, and is a gamble (not guaranteed to work). In general, I think used is better than DIY for most people, except maybe for wet/dry trickle filters. Oh, you'll need a pre-filter to remove particles from your water before it goes into your wet/dry filter (so junk won't be trapped in the bio-balls). I buy "batting" from the fabric store for almost no money, and use a paper cutter I got for $10 at the thrift store to cut it into squares that fit into the top tray of my wet/dry. Then I just throw the pad away every couple days when it gets dirty, and replace it. Batting is polyester "filter floss".