Well, as for doing it cheaply I would say that sometimes you get wha you pay for. I know I could have gone way cheaper on my stand and canopy; however I also know that they are the focal point along with my tank in my Livingroom. I want people to look at them and say... wow that is nice. Not hey did you build that yourself. As for plumbing... I have over probably close to $500 just in True Union Ball valves. I would strongly reccomend if you are doing a basement plumbed system that you invest in these since you will be taking some stuff apart later and without these you will have a much harder time.
There are many items you can save money on. Live rock, if you don't mind waiting you can pick this up from tear downs. I got about 200lbs in tear downs but needed much more. So I had to buy some. Live sand and macros are easily found along with the LR.
As for pumps, just buy them new. Take it from me.. I got one pump for my closed loop that wasnt new and wouldnt you know a seal broke and dumped 40 gallons out of my system. Luckily we caught a lot of it with a trash can but still I wish I had just paid the extra 20 bucks and got it new now.
Skimmers can go either way. If you want to wait for one long enough you may find a used one and save quite a bit. I just wanted the best so I went with a new GEO.
Controller is an expense you can skip all together. I have over a grand just in that; however, it is really nice to be able to control my system remotely if needed. (you may actually want to go on vacation some day)
Lighting... this is gonna cost some money... Even with retros you are going to have at least $200-$250 per light if you go used. I have over $1600 in my lighting but I bought HQI ballasts running SE bulbs. Now I saved by buying the reeflo 12k bulbs cause they have plenty of blue and I am not running T5. I bought all new here because I didn't want someone elses junk.
There are tons of things you are going to want but don't have to buy... these things can always wait if needed...
moon lights
wave maker
Calcium reactor
kalk reactor
media reactor
controller
all are pieces you are going to want in the end but can come on in stages....
I have over $3000 in plumbing alone, I had to run dedicated GFI circuts to the fish room (you will be supprised how fast a fish room will blow a 15a breaker) Reinforcing of the floor, mixing trash cans, QT, testing supplies, foods, there are a ton of little things that add up over time.
If you get a 200-300g done for $2k then that is awesome but I'd venture to say there are plenty of expenses you forgot about.