dave, which do you have more of - time or money?
if it's money, then the $400 is not too bad if he's going to build the filter with parts included & replace/repair any bad hoses you might have for that price. sounds like a skippy type filter which many people here use with great success. i wouldn't ever again talk to the ones that wanted $1000!! $400 is a bit steep still, but not if you don't have the time to invest.
if it's time, then you really should do a bit more research, post pics and ask lots of specific questions here and probably at koiphen. if you do post at koiphen, be sure to keep in mind that some of the people over there are a bit fanatical about their elaborate filter systems and you probably don't need anything that fancy. but setting this stuff up is relatively easy. and trying to maintain one that someone else has set up will be more confusing than if you know the whole thing from the 'pond bottom up' so to speak. get some pics of your hoses and pumps, existing filters if any, and the general layout of things and you'll probably get enough good answers to have it up in a relatively short period of time.