Yes they are truly expensive. I just purchased one for almost $500. It was worth it to me, since I figure I am going to use it through three kids (almost 4 to 7-1/2). If you are not in a huge hurry, try finding a used one on Craigslist, but be aware that they usually go quite quickly, and be sure you can get the correct shim for your size seat post or make your own.
I found the following search criteria works for searching with a search engine like google:
Of course this also brings up things like Dracula (Bran Stoker) and stove stuff (and tons of adds from people that think a stroker engine is a stoker!) but you can refine the search if you wish. I tended to leave it open so that I would not miss anything.
I did not get instructions with mine, so I had to engineer how to attach the added chain ring to my two rings already on the crank of my triplet, but after changing the chain ring spacers and going to ten speed sync chains, it all works well. My oldest REALLY likes riding it much better that the trail-a-bike that he still uses when we ride without the wife. Good luck finding one used.
Oh, by the way, a used one is a good deal if the chain rings and cranks are in good shape, as the bottom bracket is cheap to replace if necessary.
The new one that I got also came with pedals and clips, a chain, extended stem, riser for extended stem, child sized seat, narrow drop bars, and correct sized shims. There are many pictures on the web including some on BikeForum.
and several that you can find if you search the 'net.