The TI-99’s “expansion box” went for $$$, and that was before you started adding disk drives and so on. They did sort of forecast the desktop PC’s shape and footprint, though. Nice, well-built little computers. The final run was made more cheaply, though - the brushed metal was eliminated and the plastic moldings done in a putty color rather than black.
I just have the basic model with the voice sythesizer & picked up quite a few game modules, etc. at thrift stores over the years. I haven’t tried to connect it to the flat screen.