The cost is in the pump for a good quality skimmer (unless you want one of the new cone skimmers). Buy one with a BubbleBlaster or Askoll 1500 pump IMO. Those things outperform all others from what I've experienced. I'd go with at least a 8" diameter for that size tank; 10"+ is much better and the cost difference is minimal. DIY without a mill is going to be tough because you'd be much better off with a bubble plate. Cone you can probably live without unless you're into the latest/greatest. Like Bill said, deals can be had in your price range (maybe a bit more) if you keep your eyes open. I just bought a 3 pump recirculating DAS EX-3 for $240. It is an old skimmer but is licensed by Deltec and works very well. Good luck.