I don't see a price yet on the Timewave Navigator but most of their other interfaces are in the $500 range. The SignaLink-USB is in the $100 range, quite a difference if you don't really need the other features.
Yes the new Navigator is probably going to be $$$. Timewave seems quite proud of their products and their prices reflect that.
The Navigator does have many nice features that one must pay extra for. Like FSK, PTT control, Serial port output, CAT control thru USB, WinKeyer, No jumpers needed, all done thru a utility program, Front panel knob adjustment for many parameters and probably the best soundcard for digital modes builtin. It is also built like a tank, really rugged.
I paid $375 for mine in 2008 at the Dayton Hamfest. I thought it was pretty expensive but having had it now for over 5 years I have to say it was worth it.