This is a challenge. Not all that many wagons are out there that are decent for $10,000 or less. Some of these suggestions you may not be able to get at your price point.
First thing that comes to mind is a used Toyota Prius V. It is a wagon and I am sure others are going to warn you of the older model's battery pack. Yes, that is a concern. But if you can find a good one this may be a decent bet. Challenge is, below $10,000 near me I can find one from 2012 with 114,000 on it ($9,890). Battery pack should still be fine and you probably can get another 50,000 or so on it before that would have problems (probably, no guarantee). Test drive for comfort - some like it, others don't.
Older are the Pontiac Vibe/Toyota Matrix twins made out of Fremont, California at an old GM plant as part of the GM/Toyota partnership. They are pretty reliable and durable but based on the Toyota Corolla they are not the most comfortable, so definately test drive one on a highway to see if you like it. The newest I can find is a 2010 with 75,000 miles for only $7500 (FWD). It actually is not a bad choice at all if you can deal with the ride.
Subaru Crosstrek is out as it is too new and there are no units close to $10,000 yet that are old enough to qualify. However the Subaru Outback is a possiblity. A 2005 near me is going for $7985 with only 48,485 on the odometer. This car maybe even better than the used Prius because it cannot have battery pack issues. Although the engine might burn oil and you will have to monitor it (this impacts about 10-15% of all Subarus built due to the boxer engine design - also impacts Porsche). I found this car to be comfortable although I did not buy one (I bought a Legacy sedan instead later on).
Honda Crosstour is an AWD hatchback that may fit the bill. Also fairly reliable since it was not a success and discontinued, you can get one with about 100,000 miles for about $9900 (a 2012 near me with 102,000 goes for that). Pretty comfortable car which I have driven.
Harder to find but also a fit is the Acura TSX Sportwagon. There are not many of them (they sold mostly sedans) but near me there is one 2011 with 131,000 miles for $9800. These probably are going to be higher mileage and older because there are so few of them out there. It is more sporty than comfortable, but not uncomfortable to drive.
VW Jetta Sportswagon is a possiblity, but I would avoid it as it is not that reliable and in the price range you are looking, it would probably be full of issues that you would want to avoid.
Chevrolet HHR is an odd car made by GM that also probably won't be all that reliable and I would avoid. It also is a small wagon so you probably won't like it.
Although they stopped making them in 2008, there are plenty of them on the market and available. The Ford Taurus X is a possibility. It is pretty reliable (according to True Delta which agrees with Consumer Reports) and since it is discontinued is not that expensive. One with 77,000 is going for $6500 near me (and there are a lot more 2008s on the market for about that). This maybe your best bet of all as it is comfortable to drive.
So there are a lot if you are willing to go used and go old in this category. Personally I think the Ford Taurus X fits what you want - price, low mileage, comfortable ride, plenty of room to carry things for camping, car platform, and even fairly reliable (you did not ask for, but it offers it for its age).
Best of luck.