Create an Animated Dinosaur for 30 second clip

We're in the process of pitching on a job to create a series of 3 short content pieces for a museum. The brief requires a Night at the Museum style video where people explore the museum and then realise an enormous dinosaur is roaming the halls. We're looking for someone to animate that dinosaur into a live action clip, shot in HD probably on BlackMagic or RED Scarlett. We'd like to see the dinosaur as a big reveal at the end and would only need a couple of seconds animation before cutting to black. We're interested in different options so if you think you have a way of making this cheaper or more convincing e.g. just showing a dinosaur peeking it's head around a corner rather than running full body down a hall - let me know. I've put £250-£750 but really want to know how much it will cost to do this right. IF you think it's gonna be more tell me as this needs to be convincing.