Jack, for €30k I'd guess you're probably looking at an 12/18-month-old model, or a bit older for a diesel - which I'd recommend, but it depends on your usage...
I notice you haven't mentioned more economical half-way-house 'mini/compact-MPV's like the Zafira or Spacewagon, so I assume you're looking for growing room?
The Trajet is well cheaper new than the Sharan/Galaxy/Alhambra (which are all basically the same car - well, identical engine, anyway - just with a different badge on the front). I drive the latter, a 1.9TDi '01 model bought in '03, and which I hope, treated right, will drive until it drops, or until I no longer require a 7-seater! I found then that the Seat Alhambra was a good bit cheaper than its Ford/VW cousins, presumably for brand-prestige reasons, although in fact it's arguably better value in terms of finish, and certain bells-and-whistles coming as standard, whereas they're 'extras' on the Sharan/Galaxy...
Ours has had a good old hammering since we've had it and, although inside it's a pigsty, it's never given a moment's trouble, it's a pleasure to drive, and it's very easy on juice. I hear the same from the (few) people I know with a Galaxy/Sharan.
To come back to the Trajet - the main reasons I rejected it in favour of the Alhambra were
(a) I just couldn't find a suitable diesel model at the time (only brought in in 2002)
(b) it's a bit bigger inside, but it's also quite a lot bigger outside. Ask any taxi driver, they love the Trajets! But these buses can be a pig to park/negotiate through narrow gateposts, and the Trajet is a good 4" or 5" longer/wider/higher than the 'Sharambralaxy'. Also, I'd have to say that the overall finish/'feel' inside is very functional and 'plasticky' compared to the rivals.
So - it all depends on your plans/priorities! Whichever of the four options you go for, they're all solid, reliable workhorses, and a much more sensible option than the higher-priced, gas-guzzling SUV/mini-Jeep alternatives - but seriously uncool, once your kids reach the teen years...