We got the Kamei Delphin 380 from the RoofBox co back in June, very well made box and has the added security of embedded lid closure retainers.
You see so many roof box's that folk lash down with straps, so I can only think that those box's may have sprung open along the journey one time, either that or they are not confident with the closing mechanism.
The Kamei Husky XL is a good size, and you may get one of those within your budget, as they often appear in the returns/bargains section of the RoofBox co website.
I can only assume that some folk buy the Husky XL to find that it is to long for there car so can't open the tailgate hatch fully, such a box will be fine on a Passat Estate though
I'd second Kamei as a manufacturer. We've had a Corvara for 5 years and it has been subjected to a huge amount of abuse (was stored outside for 2 years uncovered as we didn't have a garage). Still going strong. Another recommendation for roofbox.co.uk who supplied it to us originally.
On our passat estate we have a Thule Atlantis .... opens either side, and locks onto roof bars via internal hand screwed knobs .... very quick and easy to mount/dismount. Here's an equivalent for 120 quid ... bargain!
Warning on delivery, I would have recommended roofbox.co.uk before but I am having a delivery nightmare now. (I have used before)
Ordered a roofbox for next day delivery expected on Thursday and l wasn't required to be in as it could be left without a signature, it didn't arrive nor did it arrive on Friday and it might arrive on Tuesday but too late for me to leave on Monday!!
So don't bother paying for or relying on next day delivery. Nice enough to deal with but still don't have my roofbox.