If you're willing to spend 2800... and shop around you can probably get about as much disc mower as you're going to get for haybine in that price range. Buying any of them of the vintage that will be at that price is like buying a pig in a bag...
The biggest concern I'd have on any haybine is to make sure the wobble box is tight and not leaking. The Deere's were somewhat notorious for needing repair in that area. Check them over for bad bearings... rubber peeling from the rollers, etc.
If you do look at discbines, just make sure that the discs are tight on their shafts. It would also be good to pull the level/fill plugs from the top of the bar and see if there's oil in it or filings on the plug. If it's clean and has oil... there's not really any more to worry about than a haybine... An 8mm allen bit usually removes those plugs.
Constant velocity joints are also a good thing to check out if the machine has one... it's an expensive item to replace if it's bad. Running the machine up to speed will tell you a lot. Bad joints will vibrate... BAD.