It's really (REALLY) easy to drill, and hole saws aren't very expensive. The bulkheads will be the most expensive part of the equation. I bought Schedule 80 bulkheads just for the peace-of-mind the extra strength offers. I'm sure the Sch 40's will work just as well, but I'm kind of paranoid when it comes to a tank full of water an plastic-plugged holes... lol! Since Saltwaterfish doesn't sell these items, I'll tell you I got mine from BRS. Saw, bulkheads, strainers, elbows, flex tubing, and gate valves cost around the same as what a decent HOB would cost. This cost doesn't include a sump or refugium, skimmer, pumps, etc...
I made a simple wooden guide for my saw by cutting a hole in a piece of plywood. I used Gorilla tape to hold it in place to cut the holes. I drilled them outside so I could use my garden hose to supply a slow stream of water to keep the saw and glass cool. I also drilled from the outside of the tank. Tilt the blade slightly to start the cut, and gradually square the saw to the glass as it starts cutting. A couple of hundred RPM's on the drill and a few minutes later you have a hole. Taping the inside of the glass on the inside of the cut will help reduce sharding at the end of the cut. VERY LIGHT pressure against the drill... let the weight of the drill do most of the work. I watched a few videos to get a general idea of how to drill glass, and it's as easy as in the videos. Naturally, there's always a risk of breaking the glass, but if you take your time, you won't have any trouble.
If you use 1" bulkheads, the saw is about $15. If you go first class with all Sch 80 threaded plumbing, use (2x) 1" Spears gate valves on braided flexible line, Loc-Line (Y, tubes, and flares) for the return, and threaded strainers, you could easy spend $200. This is a rough cost from a retail store. If you shop competitively, use Sch 40 (slip x slip) parts, PVC tubing, and ball valves, you can easily cut that price in half.
