gps + gsm

Hello,
I'm doing a project at the minute, but because i've limited technical knowledge i'm stumped. Basically what i want to do is to link an ordinary satnav with a mobile phone (type) device. The device will transmit the location of the satnav every three seconds, along with a very small amount of user-input data. The system will also receive information. One thing i want it to do is to receive information about a second location, and immediatly plot a route to it. These systems exist, but are very expensive and go way beyond the spectrum of what i want it for. I just need it as a side project to my masters.
Do you think it would be dificult / expensive to get made?
Thanks!