The 7200fx is basically the 7.2FX IIRC, and I think they "only" sold for ~$400 new. $300 is probably a little high, maybe, depending on the condition.

The 2100 is a nice ride, but it's a road bike. Sooo... depends . I wouldn't commute on a road bike, but plenty do.

I personally commute on a 7.3FX and love it. I threw a Brooks B17 saddle on it, and it's perfect. I've been riding it since March and have ~450 miles on it. The frame is a little on the stiff side - it's aluminum, after all - but it's a good bike besides that. I'll keep it until it falls apart. Has fender and rack provisions as well.

So really.. "depends". Unless cash is a huge consideration, I'd focus on the 7.3 or 2100.