I run a Kenwood tkr-820 here on i r l p, and a similar set up would work 
on echo link.  It isn't for the beginner or faint of heart.  You can buy 
these on ebay for $400 or so with duplexers if you keep watching.  You do 
need to find some one who can reprogram and return the repeater as well as 
the duplexers.  I can do this as I have both a programmer and a service 
monitor.  Then you need to interface the repeater to a computer.  I'm not 
good at building these kinds of cables.  It certainly is possible, not not 
a simple project.
73s
Butch Bussen
wa0vjr