Hey,
Glad you are hooked and looking forward to more.
I guess seperate odos depend on how much you are willing to spend.  I know we were in the same shoes when we started and where looking for a solution as well.  We even thought about another dashboard with odo for navigator, but didn't fully go for it.
Now we are using a Terra, but like you probably know, it isn't a cheap option.
However, we did use a bike speedo, running of a sensor.  But after a while they burn out (sensors that is) at least in our case.  It's either that or we just knock the whole sensor right off.  And you also have to make sure you glue the magnet to the inside of the rim.  It might work of a speed sensor, not sure never tried it, but it's worth a shot.  All I can say is that its a cheap 15$ alternative.
Hope that helps at least a bit
Cheers
Jake

I use this odo:  http://www.aminnovations.on.ca/twoam/products.html
It aint pretty, but it works...It's cheap ( i think I paid $300, and it's built by a local rallyist (Andrew Miller)  It's tough and several people have this odo who run performance rally as well.  It's definitely not ideally suited to road rally, however I have found it to be reliable and at least adequate.  Sometime when you get better you could upgrade to an alfa or something, but I  at least have no problems with the quantam.