At your price range, the best bets would be an Opel Astra wagon or a Suzuki Esteem if you want a traditional looking wagon. The Astra looks better, IMHO. Parts for either are limited to very specific dealers (you'll have to ask other owners where to shop), but ownership isn't that expensive.

The Opel Vectra might be a bit more difficult to maintain. There are many horror stories about the Vectra, both here and abroad...

Volvo parts are relatively expensive, and depending on the trim and model, might be very hard to maintain. If you get a Mitsubishi Carisma-based model like the old S40/V40, it might be a better proposition.

The Subaru Legacy Wagon may be expensive to maintain, and being a 2.0 AWD, will be less fuel-efficient than the Astra or Esteem. Of course, it's a nice car, and the AWD is good for some light trail-riding.

The easiest wagon to get would be a spacewagon. Some people complain about the fuel consumption, as it is a carburated 1.8, but I found it relatively okay when I drove one around. Though it looks like an MPV, it drives a lot like a Lancer, and interior room is very good.