It actually had a pretty huge budget, yes it was only $30mil, if it was made in the states with an A-list cast it would have cost $100. But thats because it would have spent $60mil on the cast, and $20mil on locations and crew's and all the other crap. The $30mil, was almost purely for making the film, giving it a very competitive budget in terms of effects and money to put into sets, locations and all that important malarky.
If it was $30mil done in the states with a few well known actors, then $25mil would have been on them, and the rest would have been a pitiful budget. Considering they removed all the main budget problems, location, crew, wages of major actors, then that $30mil goes a heck of a long way. Basically, the money spent actually making the film would have been the same as any other major film, just the actors fee's would have been vastly different with an A-list cast.
Take any current huge film(bar Avatar) and swap out the actors for unknowns and you'd slash 2/3rds off the cost of the film.
It was similar to Transformers in that it was style of substance, action which jumped around all over the place, while not much happened, the final fight sequence was awful, dragged out and was just flat out stupid.
The main plot points weren't strong, the script wasn't actually all that good, take out all the prawns and the lead stumbling through lines, and not much happens.