Jeff,
The expense of running a plotter isn't really in the front end purchase (especially if you're buying used). It's in the upkeep. Ink or toner for large plotters isn't cheap, neither is the paper. And, if it sits unused for a while, any ink in the thing will fail. You may need to do more than just replace the ink at that point. Plotters are kind of like old cars - run them regularly or they don't want to start or stay in tune.
I don't know where you live, but surely there's an engineering firm, architect, or some sort of design company in town that may charge a few bucks for a plot. If you can make a pdf or plt file, it will save you the headache of needing to coordinate your print settings with a specific piece of hardware.
If your town or county has its own planning or engineering department, they may be able to plot for you as well.
I work as an architect, and i can tell you that plotters usually work when you use them a lot. When you use them infrequently, they're a constant source of frustration and unplanned maintenance.
paulh