mesa boogie bass heads are damn expensive, i've seen a 400w one that was 2nd hand for $2k. i'll agree on the marshall's being average.
you may also want to look at gallien kruger and swr as good value setups. go out to parramatta rd and go to the bass player in annandale, they have new and 2nd hand gear there and should point you in the right direction, as they only deal with basses.