do you know the brand name?
chances are the insulation isnt the best in it if its not a name brand (even some name brands suck) but yea if you want to run it year round the winter will kill you, easily $100 a month to run it, especially if your using it alot. during the summer it should be closer to $50, but u can always close it for the really cold months of the winter, just make sure the lines are all blown out and u take the pumps off and put them in your basement.
how do u know it runs well? have u seen it running or were you just told?
it sounds like it wont be a bad idea if your just looking for something cheap, parts for hot tubs really arent all that expensive unless alot of stuff shits the bed at once. and labor on them is easy as well if you are the least bit mechanically inclined
if its going to get high use just make sure u either get a floating brominator/chlorinator or make sure u add one or the other at least once every 2 days, if not once a day, or it will get pretty nasty