Electron: yep, optionsxpress looks perfect for my current needs. I especially like the no fees policy, which effectively makes the service free for what I intend to use it for.
Thanks, easyrider, for the tip--I just checked out their website and saw something called the Options Toolbox. It says it's got "Simulated Position Analysis," which may be exactly what I'm looking for, though there's not much detail like screenshots, etc. Figure I'll give it a try to see what it's like. Their site doesn't say much more than to download a trial.