If you have access to a Toys-R-Us, in their "educational" section they've got some Dinosaur toys packaged as Animal Planet's "Dino Valley." There are some packs that have one big plastic articulated dinosaur and 2 small PVC ones. The smaller pvc ones have truly excellent sculpts (many were made as Jurassic Park toys originally, I think), and are of a fairly equitable scale to 28mm. You can get T-Rexes, of course, but also Plesiosaurs, Triceratops, Stegosauri, and Ceratasauri, and a handful of others. I've used a few, and they're cheap for big gaming pieces.