not abs - go with pet-g.
Less prone to uv degradation, much much much easier to works with than abs and chemically resistant to a lot more things.

And doesn't need an enclosed print volume, which abs realistically does.

If you can get an ultimaker for $899 - check it's not second hand. That's very cheap for one.

The other thing I'd recommend is a replicator dual clone. Looking around most don't go higher than 0.1mm resolution.
I know this one will - 'cos I've got one :-) http://knp3d.com/klic-n-print-3d-details/
It's rated at 0.05mm. And you could easily enclose it if you wanted to - I've never bothered.
The advantage of dual extruders is that at some point you are going to need supports if you're making buildings.
Dual extruders gives you the option of using soluble supports. So if you print with pet'g and pva you can just throw the whole thing in a sink of warm water and watch the supports disappear.

There are also filaments around specifically for printing supports with - polymaker have just released one that looks pretty good. http://www.polymaker.com/shop/polysupport/

And bear in mind that when they say pla is biodegradable, they mean if you throw it in a HOT compost heap for a few years it'll degrade. Not under normal circumstances :-)
But pet-g is definitely the way to go and if I were you I'd be thinking dual extruder for convenience.