Pre-order. The next best price is £10.93.
The first movie (the only real reason to get this set) is one of the best martial arts flicks, very enjoyable to watch.
Best of the Best 2, while not awful, doesn't have the same quality as the first. It's saved by the best characters from the original staying for the sequel.
The other two are trash. Not even on DVD before the release of this set, they're only worth watching if you're VERY bored.