I typically go the lazy route with my boxes and use screws without box joints. If you don't pre-drill the screw holes, you get problems, but other than that it works great. I can put out about 2 or 3 boxes in 10 minutes or so.
I do typically build my own frames, though it does take a lot more time. I agree with Wayne, if you are doing things in bulk, like a lot of frames at once, you arn't taking as much time in setup.
For frames I typically use a 2 x 6. Cut off the rounded top and then rip the whole board down to size. Cut the dados on top and bottom using two setups, both working down the entire length of the board. Use a tall router bit on the router table to route the tapered part of the sides and then back to the table saw for cutting out the individual side pieces.
For the top bars, at least for medium and smaller sized frames, you usually have enough scrap left from the initial rip sizing to use for them. These really take the most time setup changes. I set a stop on my miter saw and cut a bunch to length. Then I start forming the ends of the top bars with various cuts using fence and height settings. Again, do cuts that are the same for each one you are doing before changing setups.
The bottom bars I can usually make out of scrap from making my boxes. They are the easiest. Rip down for thickness and width and one nice long pass for the groove and then using a stop on the miter saw to cut to length.
Honestly, if you calculated in time for how long it takes it "might" be cheaper to buy them, but my wood working is what gets me away from the computer, so I prefer making everything from scratch.
