I have found that there are lots of videos on the web with people showing how to replace car parts. If you Google something like "video replace radio Rodeo" you might be able to find a video of someone showing you just how to replace the radio.
It sounds like your Rodeo is still running well but between having to dig into the dashboard and possibly jerry rigging the wiring to get the new radio wired right, I would be concerned that either some piece of plastic would break or that you would start having electrical problem. On some cars the radio comes out in five miuntes and only the trim needs to be removed. If your car has to have the dash removed to replace the radio then I would probebly not do it.
It might be more worthwile doing if you were going to keep the car longer but one option to get you through the next few years would be to get an FM transmitter adapter for an iPod or MP3 player. One of these could be also used with a portable CD player.
My wife has one that is something like this one for her truck;http://www.amazon.com/Philips-SJM2302-D ... ransmitter
It is not ideal but it works OK. The Biggest drawback is that you will sometimes have to reset it to a different frequency for no apparent reason.