This is somewhat dependent on what country you are in as use of the radio spectrum may be different from one jurisdiction to the next.
A system that exists today and tracks thousands of moving objects is called APRS (Automatic Packet Reporting System). It requires a radio amateur ("ham") license but that is pretty easy to get these days. It allows you to transmit the GPS coordinates (and cerain other information) to an infrastructure that already exists in many parts of the technically-developed world. You can go to http://aprs.fi/ and see all of the items being tracked on a Google Map.
There is also a proposed scheme which may be in some initial state of deployment called CSR Mesh. It uses BlueTooth-like communication into a mesh of network stations which carry the information all over the place.
But if you don't want to wait for CSR Mesh and don't want to get a ham license, you are rather limited to using the cell phone wireless network. In the USA, you can get a SIM card from Ting which costs $6/month plus whatever services you use, and you are billed for only what you actually use. For example 100 SMS messages in a month is $3 or 100MB of data is $3.
There are a variety of products avaialable that make it easy to build or buy GPS tracker solutions. For example the usual places like AdaFruit and SparkFun, and BigRedBee for APRS gadgets (and several more).