Doesn't really matter what you payed for it or when, brand new the mower was $15,000+ and so new parts will reflect it. With that said you can buy all the bearings/seals for under $100 and do it yourself or take it in for $300-400 and get it rebuilt. I done it once without major problems, Grasshopper manual provides a breakdown and any decent mower shop will provide it. The only pain I had was getting the only pressed bearing out and in, do yourself a favor too, before you take it apart draw V down the middle, parts MUST go back exactly as you take them off and the V will prevent that problem.
4000 hours isn't actually THAT bad or a gamble, my work has 3 722s/725s with 4000+ hours and none of them were well taken care of before we took over maintenance, we use them for new guys so they wont destroy the fleet of 928s and 930s we have. Out of those 3 we only had to rebuild two wheel motors, and it wasn't that difficult (just pay attention and triple check everything)
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Shameless plug for our local dealer, Doug @ Hampton Lawn and Garden in Marshfield, MO use to work for grasshopper and is a WEALTH of information, I would highly suggest you give him a call and he will set you in the right direction. He can also ship parts to your home if you want to return the love and his prices have always been pretty good for a dealer.