A good backhoe is worth it's weight in gold, especially the older ones - however there are some tricks.
1. Make sure it's 4x4 - a bigger, 2WD backhoe is a turtle on it's back when it comes to being off road. I have a 1986 JD 310, 2WD, cab, heat - but off road, it will get stuck in wet grass. They're weighted funny, so it just doesn't work well off road. However, I busted out 14inch thick asphalt with it about 3 weeks ago, doing a culvert pipe under a drive way. Saw cut it 6 inches... ended up being around 14-15 inches thick, oops.
2. Make a list of work you want to do with it. A backhoe might be good - but a mini-excavator might be better. If you're planning moving dirt around, get a backhoe. If you're just trenching / refilling (i.e. Septic work), a mini-excavator might be better. Also, how long will you want to be doing stuff? Renting is an option, but expensive with no return. If you buy something, you have an asset. But, if you're only going to be doing a weeks worth of work and you have the time to do it all at once, renting is great. If you're going to split it up and do a little here, little here - buy something.
3. Make up your mind for a price range. A good backhoe, 4x4, etc - even older is going to cost 15-20k. The 5-10k ones are going to be 2WD and pretty beat up, which means you'll be putting a lot of money into them.
To me? Mini-excavator / skid loader is the best combination you can get. And I have about everything - dozers, backhoe, excavators and skid loaders. With my ZTS 50 and 317, I never have to use a dozer, or my backhoe really. The only time I use the backhoe is traveling from my parents farm, down to my house - because it's easier to go long distance. If you can afford a mini/skid loader combo - go for it. If not, maybe look into something like a JD 110 - which is what I've been looking at to work around where I live. (Small community, about 240 acres.) So I don't have to trailer the excavator/skid loader 5 miles from my parents house. With the 110, you can get a 3 point hitch too, for various attachments such as a box blade/rear blade, etc. For finish grading.