Arduino

http://www.instructables.com/id/Make-your-own-Arduino-on-Veroboard/

Try using an lcd with SPI, they're cheap on eBay.

Systems

Power

Step Up

• $2.07 : 3v3 step up
• $0.50 : Battery Clip

Can run off a single AAA battery, good for lightweight.

Step Down

• $0.40 : Battery clips
• $0.43 : Step down regulator

Cheaper, lasts longer. I need to try using just the clips to hold a battery to board. Can also swap out the 4xAAA for a 9V. Lasts even longer, and probably lighter overall.

Display

All options are about $2. The 16x2 is a bit larger and more readable but limited to text. The 5110 is more flexible but kind of small.

Setup

Pro-Mini

$4.62

I really liked these at first, but now that I'm getting a better grasp on the stand-alone circuits, it's not as good. It takes us just as much space as the dip would, the analog inputs are hard to get to.

Stand Alone Tiny85

~$1.50

Limited IO, but that can be expanded with 74HC chips. Good for simple, small projects.

Stand Alone Mega328

~$2.00

Full power Arduino, fairly compact. I think this is the best option.

Setups

• $1.00 : Power; 9v | 4xAAA step down
• $2.00 : Display
• $2.00 : Mega328
• $0.13 : Small Perf Board

$5.13

• $2.50 : Power; AAA step up
• $2.00 : Display
• $2.00 : Mega328
• $0.13 : Small Perf Board

$6.63