BEL202 softmodem using microprocessor

This is my first visit to the forum. As Radioham I am using APRS to track mobile radios. I was using CML469 modem and works well but too expensive. I need to replace it by softmodem, in other words, decode/encode ARPS (Bell 202) on the micro itslef. I am familiar with AVR and ARM7 devices. Any suggestion?
Grat appreciated (muy agradecido)
Jorge
Pretoria (South Africa