Carlos, I've run 730/830/930 Case tractors my whole life and don't think there is a tougher tractor that was ever made. A few things come to mind:
1) The seals on the power steering ram will give up the ghost. Depending on how much you use the tractor and how heavy your bales are, this may happen once a year. It costs about $100 to have it rebuilt. If you haven't had time to rebuild the ram, and its giving you trouble, feel free to stuff motor oil into the power steering pump. Its only a stop gap, but it'll get you by.
2) Most people don't realize that the water pump has a grease nipple on it. Give it 1 shot of grease every hundred hours or so. And keep an eye on it. If its starting to get loose, get the pump changed out immediately. Since the fan runs very close to the rad, if the bearing on the pump goes out, it'll take the rad and fan with it. Rads and fans are nearly impossible to find.
3) The couplers occasionally give up. You'll need to replace the short hoses and put aftermarket couplers on it. Just switching the couplers out is tough, as the couplers have a special Case thread. You can convert the threads if you get lucky and find old stock thread converters, but they're not made anymore. And if you do find them, they're likely going to cost more than replacing the foot long hoses (where they connect to the tractor are standard swivels).
4) Rough ride. The 930 Case was called a Comfort King, and I can't think of a less apt name for a tractor. They're a short bodied tractor, so you'll feel every single little mole hole in the field.
5) Check the bushing on the front axle swivel. If the tractor has never been used as a loader tractor, its probably ok. You'll want to check it every year or two once you start using it as a loader. Its not a real difficult thing to change, but if you let it go, it'll wear the swivel on the axle.
6) If the engine and hydraulic pump are in good shape, $1850 is about right, if maybe a couple hundred bucks lower than most (I usually see round fendered 930s selling for $2000 - $2400). The hydraulic pump should be sitting at 1900 PSI. If the pump is on its way out, leave the tractor sitting. Its $1500 for a reman pump, if you can find it.
7) Something you may want to consider doing: Pull the front axle and transplant the steering axle from a combine on it. The power steering pump will give enough pressure to run a ram. My 930 is hitting into the shop this winter, and I'm transplanting the power steering assembly from an 8600 White combine.
8) A must do: Put a good grill guard on it thats attached either to the loader or to the front subframe. The rad attaches to the sheet metal, and if you bump the front grill against a trailer when you're loading bales, it'll probably drive the rad back into fan blade. This is a nightmare to fix as it'll bugger up the rad, the fan, and likely the water pump. Please don't ask me how I know this.
9) Keep the clutch brake adjusted. Its not often that I've had to do it, but without the clutch brake, changing gears is difficult.
I think thats about it. Hope it helps.
Rod