Cheapest Arduino GPRS or 3G solution I am looking at creating a fleet of low power, Arduino driven devices.

I would need some kind of GPS on them all (or could triangulate through phone network?) plus a connection to the internet - just for HTTP POST requests. GPRS or GSM would do but 3G would be better.

What are the best (price is a major factor because I'm trying to do a fleet) GSM, GPRS or 3G modules that I can use with Arduinos? As I said, I need their location so one with GPS built in would be great.

EDIT:
The amount of devices in the fleet will change, so the entire network needs to be dynamic which is why having a GPRS/GSM module on each one would work so well.
If you are finding Cheapest and working module you can you SIM800L less then 4$. 



aliexpress.com/item/Free-Shipping-Smallest-SIM800L-GPRS-GSM-Module-MicroSIM-Card-Core-BOard-Quad-band-TTL-Serial-Port/32708504554.html


You can find many other cheap alternative but they does not work properly.

Sim800 have good support and you can find many examples to use this with arduino.

Many other model also available in market as per your requirements.