I was reading old magazines in the "reading room" the other day and came across a shop-built router lift plan in an old issue of American Woodworker. (Maybe 2002?)
I can't say I agree with all that they did in the plans (I would epoxy the bronze bearings into place), but all the ideas are there to utilize the same carriage as a micro-adjust for a router table fence, tablesaw fence, drillpress table fence or any number of other things. (I'm planning on using the idea to move a thread cutting jig I'm planning for my lathe across the bed to align it correctly with the cutter.)
The 3/4" steel rod makes sense for the router lift, but for some of the other ideas even 1/4" steel rod would suffice. Therefore smaller bronze bearings and lower cost. And the amount of steel rod and length of carriage needed would be based on the application. No need for 18" of travel for most.
Anyway, long story long, the plan is up on the Popular Woodworking site. Thought others might find it interesting as well.