A lot of the more expensive Essex ones are quite hefty; the Cursaa's orcs are much bigger and heavier than the Citadel orcs of the same period (maybe around twice the mass). So the amount of metal is probably a factor in the price. I think most of the Olley ranges are quite chunky, and so are the great scaly orcs.
The goblins aren't bad value at three for £3.85.
The Minifigs fantasy range are quite expensive; I gather they're quite tricky to cast, given the age of the moulds. I'd love to see more of the range back in production, though - they're really charming.