Having just done a bunch of research into the exhaust before ordering mine here's some info. Yes Toyota used metal gaskets between the manifold and y-pipe. However, they were designed as crush gaskets, meaning that properly torquing the y-pipe to the manifold will crush (and slightly deform) the metal gasket in order to ensure a seal. Reusing a crushed gasket will likely end up with an exhaust leak. You could try to over-torque the bolts if you like to see if the gasket would crush more making the seal, but that's iffy at best. Why not just spend the money and replace the gaskets? You can check a box when you order the URD Y-pipe to add the pair of gaskets for a whopping $10.
As for the gasket between the manifold and head, yes it's more expensive, but that should be replaced as well for the same reasons and more. An exhaust leak into the engine compartment ahead of the cat and AFR/O2 sensor means your mixture isn't going to be correct. Not to mention you're heating up your engine compartment, and not everything in there tolerates heat well.