Bought a new manifold for my SMTA last summer for $145.00 so you're not to far off there. Decal set seems pretty high though. Have seen them advertised as low as $25.00 but have heard of guys paying up yo $85.00.
What really matters is what they are worth to you. Apparently at the time you felt they were worth the money or you wouldn't have bought them.
Don't go second guessing yourself, there's always going to be somebody who gets something bought cheaper or sold for a higher price. I recently heard of a SMTA selling at auction for almost half what I gave for mine so I know how you feel but what's done is done.
Go put them on and enjoy your H