I meant to add a summary of the absolute cheapest way you could try APRS.

Assuming you have a PC and a radio you just need a cable to hook them up. If you only want to receive and decode packets you need to connect the radio speaker output to the PC sound card mic. input. If you want to transmit, you hook up the PC sound card speaker output to the radio mic. input, and connect a transistor driver from a PC parallel or serial port line to the radio PTT. Here's a simple example [1], but there are many designs on the net. Such a cable would be extremely cheap to make, and software of course is free.

Naturally, you will need a station at the other end, although it's very Zen to ask "what is the sound of one APRS station transmitting?".

73!

[1] http://www.qsl.net/wm2u/interface.html