If you're looking for inexpensive mecha for your tabletop gaming, check out Dollar Tree.
The Transformers line of toys are now in the toy department while supplies last. Note that from what I have observed, availability is spotty, so it depends on each store.
These figures do not transform, and are not pose-able. The main figures are composed of a rubbery material, but some of the added parts seem to be standard plastic.
This is Megatron, leader of the Decepticons. In the original cartoon, he was 19.6' tall; in the movies, he's 35' or 38' tall. The toy is 2.125" from foot to top of head, making this figure roughly 15mm scale (cartoon) or 6mm (films). Of course, if you decide he's not Megatron, he can be any size you want him to be!
The figure is stable on its feet. The black gun is his Fusion Cannon, which as modeled here lacks an opening. The 'smokestack' on his back is possibly his jet booster.
StarScream is Megatron's second in command, and was 16' tall in the classic series, and 31' in the films. The toy is 2.25" tall.
The small feet are not large enough to keep the toy stable. His only visible weapons are missiles on each arm.
These are the only two toys I've seen so far, but your luck may vary.