The monthly fee is 12.95 I believe, and you can buy a Mondain's Legacy upgrade code on ebay for real cheap. I think I saw one for 10 bucks?
Anyway, with AoS you can pretty much access anything you remembered back in the day still. There are certain areas, items, and things you can only do/have if you upgrade though, but most of it is arbitrary. I was in your shoes as well. I got back into
UO after a 3 year abscence at the end of June and didn't know anything going on.
I moved to Atlantic because everyone I knew from my old server was gone, and the reason being was because was that I get the best ping on Atlantic, ironically, and there are more people there to interact with. As for housing, it is still relatively cheap. If you get about 100k you can buy almost any decent sized house. The hard part is finding a spot to put it in. If you don't care what size house you have initially, then you can find a spot pretty easily. I just found a plot near the yew gate in Fel on Atlantic that was 9x14, so it is possible to get a decent sized house in a good area still.
The 2D client is still what I use, and yes, it is still quite good. Most screen shots that you see are from the 2D client.