B.E.
My house came with a hot tub - at the time it was probably about 14 years old. I thought "What the heck am I going to do with a hot tub?" I was much more excited by the in-ground pool. Now, 17 years later, I use the hot tub far more than I ever use the pool. I keep it open all winter long and, for the most part, maintain it myself. There are pretty simple chemical kits for testing the water and the company I use for repairing the tub basically told me all I ever need is a PH balance chemical for whenever I refill the tub and bromide tablets to keep the water clean.
In my opinion, you will need a hot tub cover (especially to keep the heat in, and also for safety if you have young kids). They run anywhere from $400 - $600. You will probably also want to have a hot tub company come in and look it over and give you some advice before running it the first time. Since my tub is getting pretty darn old now, I usually have to have the repair company come in once a year to do minor repairs. I think I generally spend around $200/year for them.
For me, probably the biggest expense is the electricity to run the thing - something to keep in mind. Some people have units that run on alternative energies, but mine is electric.
Although my experience has been positive, my father had a terrible time taking on a used hot tub. The person he got it from had overdone the bromide which ate through a lot of the fixtures and they had also kept it in a rodent infested area, so many of the wires were chewed through. He poured a couple thousand into it and unfortunately had to dispose of it in the end. He does miss having a hot tub, though. They're great.
