Aneuploidy:
I'm no expert on the used market, but that's a pretty low budget for a tractor and a brush hog. If you don't mind walking I would recommend a DR field a brush mower. I have a 17hp 30" (I also have a 3720 cab, 2305, and a 5' LX5 Brush hog).
The DR will 'out cut' my 5' brush hog as it's rated for 2.5" (And I've exceeded that) and the brush hog is rated for 1" (You can go more if you want). The DR is blades first and makes cutting the rough stuff easy and you cut first rather than run the stuff over. It's got only a 30" cut compared to a brush hog so it'll take you longer. Also, I'm assuming that most of the 'woody' stuff is a one time cut and you won't be repeat cutting it. If that is the case you might also consider renting a tractor/hog for the big first cut, then using something else for maintenance. For reference my lot is a little over 6 acres and I have another 2.6 acre lot. About 1.5 acres, maybe 2 of the 6 acre lot was all woody saplings and brushy crap that I've cleared. I did ALL the initial clearing with DR (Before I bought my tractor). FYI, when I got my first tractor (the 2305) I didn't even get a brush hog as I had the DR.
I rarely use my 5' brush hog unless I"m out hogging a lot of brush the snowmobile trails or occassionally if I let the areas I've cleared get way too long for my finish mower on my lot. For my lot I mostly use the DR unless I have a huge 'brushy' area. For woody areas I usually use the DR over the Hog. (And, yes, you can back up with the brush hog and cut first but it's not as easy as just driving forward).
You could buy one new for less than 3K and I'm sure you could get a used one cheap.
Maybe I'm wrong but I can't imagine you finding a tractor/brushhog combo for that price range. Maybe if it's very, very old.
Now, don't get me wrong, there are 1000's of other reasons to buy a tractor..

but I'm just thinking what fits in your budget.