I own a vinyl shop - your best bet is to get a blade holder on ebay (search roland blade holder) - they ship from china for about $10 each, and then get some Clean Cut Blades - best blades out there (cleancutblade.com). I've used one, daily, for a year, and its still sharp.
You'l have two issues to take into account however. Pressure is one... the shapeoko has no real pressure setting. Its not just a matter of distance down, its a matter of how much pressure you're applying. Maybe mount the blade holder with a spring so that once the Z is down, the spring pressure keeps the blade into the substrate?
Second is offset. Blades spin in those holders. Say your shapeoko it cutting "north", then the head picks up. The blade will be facing north.
You then move, and go to cut a line going "west". The blade is still facing north. The tip will enter the substrate a fraction of an inch "south" of your cut, and the end of the line will have a small curve to it as you start moving "west" and the blade corrects itself.
Pro cutters take this into account, it's called offset - it's how far the tip of the blade is from the center of the blade and how much the machine needs to correct for it. Its not really an issue for large shapes, but small, complex shapes will be nearly unusable unless the offset it correct.
Here's a really bad MS paint illustration of what that cut would look like:
- bad cut.jpg (1.74 KiB) Viewed 2184 times