After research, how should I go about creating a bluetooth peripheral?
The Bluegiga/Silicon Labs BLE113 is quite small:



and can be purchased from Digi-Key for $13.78 in single quantities.

It is a BLE 4.0 device and contains an integrated 8051 and can be programmed in a BASIC-like language called BGScript.  I am currently doing a project with one of these and it communicates successfully to an iPhone.  Bluegiga has free example source code for both iOS and Android on their web site.  You just have to register.

The current draw is very low; the transmit current is spec'ed at 18 mA max but when I measure the current when connected to the iPhone the average is only around 2 mA since the transmit duty cycle is so low for BLE.  In sleep mode it draws &lt; 1 µA.

It has lots of general purpose I/O pins available, plus I2C, SPI, PWM, and UART interfaces.

The development environment is free, but you need to get a programmer.  Bluegiga has a couple of different development boards that work with the BLE113, but they start at $200.  I suggest instead you get a TI CC Debugger, which is compatible with their programming software.  You can get one from Digi-Key for $50.



For prototyping, to avoid having to solder the surface mount BLE113 modules I got these breakout modules from iNMJO for $40:



which include the BLE113 plus a 10-pin header that is compatible with the CC Debugger.  The board is still quite small, 1 1/4" x 3/4".