How to make GPS/GPRS tracker and real-time updater cheaper?

I'm getting started with Arduino and want to make a portable, slim, gps tracker that gives real-time updates and activates either when the object leaves a "safe zone" or when it's texted by a phone.

A stretch goal is for the device to emit a high pitched tone, or other alarm sound notifying people passing by.

It seems I need the following parts:

  • TinyDuino $20 - Eventually, only a "lilyboarded" ATMEGA328 chip for $3.
  • GPS/GPRS module $60 - Obtains Positional Data/Connects to internet to relay information in real-time.
  • Antennae X2 - Two needed for GPS and GPRS?
  • SIM900A or SIM809 - Allows texting and 2g or 3g data using pre-paid SIM cards. Essentail for real-time updates and text abilities.
  • Power Source - 3.7V Lithium Ion battery
  • Container - TicTac for now.
  • Misc. case parts
  • Speaker module - Optional

I've found a few tutorials, including this one I want to start with, and this one that has real time gps/gprs, but the parts are always over well over $100...

Questions: 1. How to make it cheaper?

How can a device like this one be only $13 and do the same things? Is there a cheaper way to do this or is it just because they are sourcing parts directly from cheap factories in China? It's tempting to buy one and reverse engineer the pieces...

  1. Do I REALLY need to by two antennaes?

  2. Is there a way to use even less parts to get the cost down? I'm asking because there may be devices that accomplish similar things I'm not aware of as a newbie :)

SIM908. GPS/GSM/GPRS all in one. Still need two antenna (one for GPS, one for GSM/GPRS), it's fairly large (forget TicTac!) and power hungry. But that applies to most GSM/GPRS boards.

Ahhh yes! That is exactly what I needed to hear :) Thanks for the clarification. It is a lot of info to take in, but the SIM908 is clearly the way to go!

my phone has a GPS, is thin and lasts for a full day on a battery charge. sometimes 2 days. not sure what is used in the phone, but small for the antenna is possible.

here is a child locator : http://www.amazon.com/Mommy-Im-Here-cl-103br-Locator/dp/B0009PLRXK

smaller if you loose the blue teddy bear