Costs are going to depend on what shelving and shelving support material is used, but a good ball-park figure would be around $15 per 4-foot shelf, assuming you're starting empty handed.
This was one of those projects I thought, "Hmmm - I think I should be able to knock those out over a weekend" -aaaaaand I was wrong. I ended up going down a few dead-end roads while coming up with a design and process, wasting several days. I'm hoping that you can benefit from my mistakes ;)
Here's the materials list:
1. Shelving material - in this case: 3/16" x 8" wide tempered glass shelves in a couple of lengths from a local commercial display store. Do not use plate or standard glass - it's nowhere near as strong, and if it breaks it is very dangerous. Tempered glass is anywhere from 5 to 6 times stronger than standard glass, and if it breaks it shatters (completely) into kind of glass "gravel". If you've ever seen a shattered car side-window, you've seen broken tempered glass. Polycarbonate or plexiglass would work, too, but would probably be more expensive and not hold up to use very well (dusting it can scratch it up).
2. Wood stock - I used Purpleheart, Philippine Mahogany, Poplar, and Curly Oak. Stick with hardwoods - softwoods probably wouldn't be strong enough to hold up to any kind of weight. Poplar is considered the softest of the hardwoods and would be as soft as I'd be willing to go.
3. Aluminum angle - I used 1"x1"x1/8" stock purchased at a home improvement store. Make sure to use angle suited to the thickness of your chosen shelf material - i.e. if you use thicker shelving material buy angle with longer "legs" so you have enough to attach to the support.
4. Keyhole hangers - I bought a few at a local store and then more from an online retailer (much cheaper online). Be sure to buy the heavy-duty hangers and also be sure to have your keyhole hangers in your hot little hands before you decide how to machine the slots in the back of the supports. Keyhole hangers vary widely in their overall dimensions depending on brand, so a slot that fits one, might not fit another.
5. Screws - Yes, the hangers come with screws - as does most hardware - and as with most hardware the screws are pretty cheap and weak. I bought better quality screws (#6 and #8 for the hangers and #8 for the "glass clip") as cheap insurance.
4. Finish of your choice - I used a good quality laquer. Since these supports don't get much direct handling, almost any finish would work just fine - paint, rubbing oil, polyurethane, naked, etc. Lacquer dries quickly and is reasonably durable - so it got the nod for this project.
While you really don't need a full shop to build these, it definitely speeds up the process. If you were patient, you could build these with a drill, cross-cut saw, coping saw, hacksaw, and a collection of files, rasps, chisels, and sandpaper.
Step 1: Plans and Stock Preparation
I want to stress that the design of these shelf supports can be adapted and changed pretty easily. The only thing to keep in mind is that the center-line of the anchoring screw (the one coming out of the wall that you'll be hanging these on) should probably be kept above the vertical center-line of the shelf support. You could make these taller, deeper, wider, or whatever depending on your needs and aesthetic preferences.
After thickness planing stock to the same dimension (to keep setup consistent), I ripped the stock to finished width and set up the miter saw for cutting lengths. Unfortunately, the only blade I had on hand was recently used to cut a bunch of laminate flooring when I helped a friend put in a floor - which is about like cutting concrete blocks with the saw - so it was too dull to be very useful. This, however, gave me the opportunity to show a technique for safely cutting lengths on a table saw.
Disclaimer: You'll notice I don't have a blade guard on my table saw - and to be honest I don't know how people work with a saw WITH a blade guard in place - but to do the obligatory C.Y.A. I have to say that you shouldn't use a saw without the guard. Personally, power tools have my deepest respect - respect tinged with fear - so I tend to take very, very few risks. I prefer that my body parts remain attached.
The best way to cut short lengths on a table saw safely is by using a dedicated "sled" - but I lost mine in the last move, so I had to go with the close second: using a spacer board clamped to the fence. The spacer board should not extend any closer to the front edge of the blade than the width of the stock you are cutting, and should be set a bit further away - you want no chance of the workpiece binding between the blade and the spacer board, or, the blade and the fence. Use a push-stick as much as possible and just keep your head about you when using any power tool. Never be reluctant to sacrifice a piece of stock - no body part or injury is worth it.