When it comes to things like this, especially with your missus, you have to take it.
She was expecting you to be over the moon. I mean, I am assuming she knows you'd prefer a Transformer over cloths, so she's done something really nice and got you a Transformer. Even though the price wasn't a good one, how much you save getting it else where? What 5, 8 bucks? It is also her money, so you aren't spending anything, you've saved 27, gotten a Transformer, and most importantly, made her happy by the excitement/joy you get from her gift. It is a Win, Win, Win situation.