Someone had asked me about the total cost, and how it compares with commercial units. Since the question requires an in-depth reply, and since I tend to write novels for responses, I figured I would share with HaD community.
Total investment is hard to say... the electronics cost is quite small ($35 for the Teensy 3.1 microcontroller + Audio board, $25 for my custom designed PCB, maybe another $60 for the rest of the components and RCA connectors / cables (the connectors / cables are from eBay, the components from Digikey).
The frame is where things get fuzzy - I bought the frame years ago from a local classified ad for $50, but trying to find all the same stuff new would cost much more. Likewise, I already had the two bass pedals (one for bass beater, one for hihat pedal) from my previous sets. There are some alternatives to the frame, of course; I found that electrical conduit can work very well for it, although it is heavier than the aluminum that I am using now. Still not sure what I would use for joints / connectors for the drum pads in that case... and the commercial drum clamps are expensive (around $30 each these days). I had some from years ago, and connected some of the pads directly to the frame (the two top cymbals and the bass pad are done like this) so I didn't need to buy any more.
The pads are quite straightforward - I used cedar fence slats, planed down and butt-jointed together, as the material for the rims. Plywood probably would have been better. A single 4x8' piece should be sufficient if I remember correctly; budget about $40 - $50 for this (you would want to use higher quality plywood, I assume).
The drum heads were cheap - $5 each for Pearl Muffle Heads, obtained pretty much anywhere. I bought mine locally (and already had a bunch from before, so only needed to get a couple more this time), but you can find them online for the same price.
Then there are the misc. screws and fasteners, which I had in my inventory already from previous projects, but which would have cost around $20 - $30 if purchased separately. Then of course there is the cost of tools if you don't already have those (both for the electronics and the woodworking side of things).
So in summary, for me, my total investment in this project (i.e. the Drum Master 2.0 revision) was around $100 - $150... but there was a lot of other sunk costs from my previous projects that I leveraged, which is not counted here. I really can't say how much it would cost for someone starting from scratch, but I doubt that it would be much cheaper than an entry level kit. I build things because I love to create; for the most part my creations cost more than they would have if I just bought an equivalent, but then I would not have the experience and knowledge.
As for how it compares... I would say that it compares quite favourably with sub-$1000 kits. My kit is easily extensible (it has connectors for up to 11 pads, plus one hihat pedal and three cymbal mute switches). You can pick your own samples (this can be a pro or a con depending on your point of view, but most cheaper sets that I have seen don't let you do this). The sensitivity and consistency is quite good, with a dynamic range from soft ghost snare hits all the way up to really banging on it. The pad sensitivity calibration is done via software (I use software-controlled potentiometer chips to adjust the amplification levels, so it is easy to calibrate different pads). I do not have positional sensing; i.e. I don't play different samples for center vs. edge on drums, or bow vs. bell on cymbals. My hihat pedal senses position, and I can play different samples for different positions plus the 'chic' sound when closing. I had support for foot splashes, but got rid of it because I didn't like how it was working (and I don't really use it in songs). I am not really familiar enough with current sets to say much more than that... my previous commercial set was an old Yamaha from about 10 years ago, and this one is far better than that one (both from a software perspective as well as an ergonomic perspective), but I know that commercial sets have also improved greatly from then. I have played with current sets in local stores, but not enough to be intimately familiar with the pros and cons of them.