Ponygirl,
I don't have much knowledge on the John Deere rigs but I do want to emphasize having a large enough tractor. (example) I purchased a TC21D New Holland which is about the same size as the 4100, maybe a little bit bigger than the 4100. I used it for mowing lawan and moving dirt with a FEL. I found that you couldn't move much dirt with the TC21D. It was just too small and even on level ground with too much dirt in the bucket you tend to take the back wheels off the ground and if you turn sharpe with the bucket up the tractor would start to tip over. So any way I ended up biting the bullet and taking the tractor back and I got a TC29D. I believe manure is heavier than just plain old dirt so you would tend to have more problems
Anyway another option would be to look for a little bit older tractor that is larger in size that you could get for less money, one that was taken good care of. Also you may want to look at some of the other tractors out there. When I was looking I was set on buying a JD4100 used, but then I checked out the New Holland dealer and I ended up getting the TC21D brand new for about $1,000.00 less. I also ended up trusting the dealer a lot more also. So even if the New Holland would have been more I think I would have gotten it yet because of the dealer.
Well I am starting to ramble here, I hope this helps you.
Murph
ps: my neighbor did buy a 2000 JD4100 with about 250 hours on it. It had a MMM, front blade, snow blower, turf tires Hydrostatic and he paid less than 11,000.00 delivered