MDF/partical board made shelves will sag without support under the shelf. Period. Plywood will also sag, usually less and usually does not need as much support.

That support can be fastening the shelf to the backing materail and adding a front trim/support piece.

You can buy cherry plywood---although it will cost upwards of $90 a sheet. To do veneer correctly, a vacuum press is needed--and a press of that size will be very expensive.

Staining birch ply will be the most cost effective, but the quality of the finished stain depends a lot on the quality of the birch ply and the expertise of the person doing the staining. A wipe off stain is probably the best with which to learn, since controlling the color is easier.

BTW, those units from the office stores are hi end only because of the finish, not the construction, IMHO.

Just finished building a couple of shelf units usung 3/4" plywood. Cut the shelves 1/2" less depth and glued and nailed a 1/2" strip for face to make it the desired depth.Used a 1/4" plywood for the back. Used solid wood for the vertical supports with little blocks attached inside supports for shelves to rest on. Used an Olympic stain (Merlot color) similar to dark cherry with possibly a little more of a purple tint, and a couple coats of semi-gloss poly. I used crown molding for the top as you talked.

I agree with HandyMac, use plywood.

The client was very happy with the look.

I just completed a very large entertainment unit for my own living room. Although the design is different from what you've described, the technique I used could give you the strength you're looking for at a reasonable price.

If you're thinking of painting the visible portion of the back, you could go with a $15 4x8 sheet of 5/8 BC plywood, sand it, then stain with the same stain you use on the rest. If it isn't going to be visible, I'd probably start with a 60 or 80 grit and finish somewhere at 120 or 150, but no higher. You might want to look at 1/4 inch tempered hardboard, if price is really an issue, but bear in mind that tempered hardboard has the same limitations of MDF.

For the shelves, I'd build a small skeleton for each shelf from select grade pine (or inexpensive hardwood) 1x2's, the same width as the interior dimension of the shelving case, and rabbet around the inside upper edge of the frame, to place the plywood shelving material. Make sure that with a height of 7 feet, you have two of the shelves fixed in place, for stability.

For something this size and purpose, you'll also want to consider a torsion box construction for your verticals. This is essentially a sandwich of plywood on either side of a 1x2 frame. This is then fronted by some nicer looking solid wood.

For the basic structure outlined there, you can probably get away with more inexpensive materials (sticking of course, to wood and plywood.), and based on how much wood you need, and what I spent on my last projects, you're looking at anywhere between $200 and $300 USD. Considering the quote you mentioned, this is a bit more reasonable. Once you've got your basic structure built, you can start looking at more expensive facing material, perhaps even solid cherry for the fronts of the shelving and vertical members. Not sure what cherry is going for, I've not any experience with it, but if you stick to buying only what you need for the exterior, cosmetic elements, it shouldn't be too much.