The Rigid is an excellent machine, worth saving up for. If you go the way of a disk on your table saw, I would suggest that you replace the insert that goes into the opening in the table top with a zero clearance insert. You can get them from anyplace that sells saws and accessories, or you can make your own using a good piece of plywood. The idea behind a zero clearance insert is to prevent wood from being pulled down into the gap between the insert and the disk. Shape it to fit the opening, using the original as a template. It will likely need shimming to make it flush with the surface. You can glue small bits of wood to the underside until it's flush. A small nail driven halfway into the end that faces away from you when sawing will stop it from rising up due to the rotation of the blade (sanding disk).
Cutting the slot can be done by lowering the saw blade all the way, then placing the insert into the opening and firmly clamping it down at both ends so the blade can't touch the clamps when you raise it. As you carefully raise the blade, it will cut a slot in the insert. Just stop when the slot is big enough. You may have to widen the slot some. You want it close to the disk, but not touching.
If you're not comfortable making your own insert, it may be worth buying one. They're not too pricy.
I hope this helps and if you have any questions, I'll do my best to answer.
Dave.