Don't let all the included implements, as nice as they may be, confuse the sale. If I had to guess, I would price the implements at:
Bush hog - $250-$400 depending on condition and size (4 or 5 foot)
Disc - $300-$600 depending on condition and size. Could be worth a lot more if it was in great condition, but probably isn't.
Box blade - $300-450 depending on condition and size.
Scraper blade - $300-$450. Could be worth more if it was large, heavy-duty, or had hydraulics, but it probably doesn't.
Middle Buster - $100-$150.
Broken post-hole auger - $0 - depends on how it's broken, but if I was buying it as a package, I wouldn't give much for it.
So, by my math, you have between $1250 and $2050 in implements. On the one hand, you won't be driving all over kingdom come to pick them up off of Craigslist, but on the other hand, since you're buying from a dealer, you'll be paying sales tax, which you most likely wouldn't on Craigslist, so let's just call that a wash.
Now, looking on TractorHouse.com, around $10-$11k seems to be the asking price, so you may be in the ball park here if you count the implements. With a $1-2k credit for the implements, that brings the dealer's actual asking price down to around $10-$11k. So is it a great deal? No. Is it a rip-off? Probably not too bad. But those are just asking prices, right? So you should be able to talk the guy down maybe another 8-12% I would think. Depends on how bad you want it and how bad he wants to sell it.
Not sure how you other guys are getting "just a few thousand more" for a comparable new tractor. I just went and built an L2800 on Kubota's site. With the standard FEL, it came out to $18k and change. Compared to $10k, that's a lot more than just a "few thousand".
EDIT TO ADD: Any of those implements might go for two to three times as much if they were in brand new condition. But they probably aren't. And even if they are, then I would just say to the dealer, "Fine. I don't want it. Take $X amount off the price of the tractor," and I would make sure that $X was darn close to retail for the item. My perspective is that there's not a lot of sense in buying brand new tractor implements unless you just really like being the first to knock the paint off something. Maybe with a mower, where it may have been abused or damaged in the past. But a box blade? Please. If it's square and it isn't rusted out, it's probably fine. So don't let a dealer try to put one over on you by "packaging" new implements in with the tractor that you wouldn't have bought anyway. The one exception there, IMO, is if you need to put the implements on the same financing as the tractor. If you just don't have the cash, and are willing to paymore in order to get them today, then go for it.
Frankly, package deals of tractors with implements really confuse the issue, I think, and work in the dealer's favor. It's one thing if you're buying retail, and can look at the price list. But if the implements and the tractor are used, you can end up paying more for the tractor than you ought to. Far better, IMO, to haggle with the dealer on the tractor's price ALONE and then, once a fair price is arrived at, move on to buying the implements if desired.