Currently I have only found one (commercially produced) automated sprouter on the market, and it costs ~$180 for just over 1sqft. of growing area. The growing area for this sprouter is ~4.25sqft and cost me ~$50, although I did have a majority of the parts in my garage. If you were to do this as conservative as possible I would estimate you could do this project for around $70 assuming you use recycled take-home (to-go) restaurant containers for seed trays and find a bin to do this in around the house. You could reduce the cost even further by checking garage sales for irrigation timers, and valves.
Step 1: Gather Tools and Parts
A bin with lid (I used one ~34" x ~18")
Mister kit (Orbit 20066 Portable 1/4-Inch Outdoor kit)
Irrigation valve (recommend 3/4" so you don't have to adapt it too much)
Irrigation timer (make sure it has at least 6 daily start times)
All appropriate adapters to connect your system to your specific water supply, and interconnect all components you choose
Whole house water filter (Culligan HF-150A, or Omni 0B1)
Carbon Cartridge for above mentioned filter
Calcium Inhibitor filter (WaterSentinel WS-21)
Razorblade / SHARP Knife
Drill and bits
Step 2: Install the Mister in the Bin
After the holes are drilled remove all of the mister nozzles, and T-sockets from the water line they come connected to. You can do this by pulling back the retaining ring (may need pliers) and then cutting the line with a razor, and bending the hose to push the barbed connection out the side of the tube (as pictured). You can then use the remnants to reconnect these at the correct width to mount in your bin. Start from one end (considering which end you want the water line to extend from) and put a mister in. Attach one of the remnant pieces of hose (saliva, or water will help), and cut it to length to extend to the next hole. Connect another T-socket to this hose, and install the nozzle. Repeat these steps until you have all your nozzles installed.
Step 3: Install Drain Hole
Now if you have a piece of tubing that fits on the threads, or you plan on just letting it drain into a pan below you are done. For my situation, my tubing fit on the cap, but not on the threads. To make this work for me, I just drilled a hole in the cap, and then slid my tubing onto the cap. This gave me a detachable piece of tubing from the bin that allows easy cleaning.
Now drain into something, or outside to your planter
Step 4: Connect to Your Water Supply
Fit all of your parts together, starting with whatever you choose for your supply line, and finishing with a 1/4" high pressure water line connector. The sharkbite quick connectors are great for this.
My setup used:
1 male hose to barb
1 female 3/4 hose to barb
1 female 3/4 hose to 3/4 pipe
1 short 3/4 male to 3/4 male pipe
SPRINKLER VALVE ->
3/4" male to 1/2" female adapter
1/2" male to 1/4" sharkbite quick connector
1/4" supply line
Adjust yours accordingly
Step 5: Get Some Seed Trays
The white trays pictured are available from http://www.greensmoothie.com/sprout/gogreen.php (the inspiration for this instructable)
Step 6: Program Your Timer
If you need a place to get seeds, try sproutpeople.org They have excellent seeds, and selection, and incredible support for thier product. All of the harvest times for every seed/variety they sell is posted, and a lot of videos as well.
Be sure to leave the lid cracked open approx 1 inch when sprouting. You could probably put ventilation holes in the lid with screen glued over it as well, but I haven't tried it yet.