When you see the amount of torque generated by the plunge bars on the router mechanism, you'll realize that this is not an application which would allow for flimsiness.
Used DeWalt 625s appear all the time for sale on eBay for significantly less than $100, so why invite trouble. Among my routers I own a Festool OF 1400, and I would prefer to use it on the WR because of excellent dust collection. But no plunge bar is made for that model. I've seen homebuilt contraptions on a few websites, but they look unreliable.
Moreover, contrary to what the folks at WoodRat might say, mounting and dismounting a router on the machine is NOT simple as 1-2-3. You'll want to have more than router. Use the router you've got for freehand routing, and buy a dedicated router for the WR.