One thing I learned about buying an older tractor is the lack of attachments - especially mid-mount mowers - that are left in usable condition. So, if you're going to get something like the 6100, which I think is an early-80s generation machine, be sure to buy one with the attachments you want already AND be sure they're in good enough condition to require only regular maintenance. I bet that's going to be an unlikely combination.
I think $10k is the sweet spot for a BX-sized Kubota with a backhoe. It's depreciated about as low as it'll go - someone always seems willing to spend $8-10k, so you can regard the thing as your savings account if you can afford to pay cash. Seems like you'll have a lot of options at that price-point. A lot fewer at $5000 or less.
Also, have you considered getting a real piece of equipment - i.e. a well used
B20 - and getting the jobs you want to get done over the next year or two and then selling it for pretty much what you paid. Then you can get a more appropriately-sized unit like a BX-series for your property for the long term?
Finally, if you're going to go new, be darned sure that you're buying what you need - not what you think you want at that particular point in time. Your property isn't going to grow or shrink (obviously, unless you sell your place). But, the decisions you make about what you're going to do with it might. This is that danger of buying new and presents the possibilities for a serious pitfall: trading in for something different when you realize what you bought isn't doing the work for you.
So - to sum it up - I say, if you're new to tractors, buy your first one used. And just like a classic car, buy as expensive, recent and well-serviced machine as you can find/afford. Better to pay $1000 more for a better unit than roll the dice on one that's cheaper, but condition is unknown. This way, if you find it's not doing the work you need it to, you can sell much closer to what you paid for it than you can a new one. Simply put, if you get a brand new BX and it turns out not to be cutting it, you'll be out an easy $2000+ when you try to sell it, simply because that's the minimum difference in cost that anyone would be willing to pay, given the current 0% financing deals.
