30 day stay in Germany

It sounds like you need to rent an apartment or home. I haven't used them but have heard good things about vrbo.com http://www.vrbo.com/vacation-rentals/europe/germany#a6202

Do you mean within the State of Hessen and 30 miles from Frankfurt? Or do you mean with 30 miles of Hessen? Are you using the rails to travel into Frankfurt or to other places (where?) or both? How frequently will you be traveling? It's tough to suggest a strategically-located base or transport tips without this info.

We would be staying in the Frankfurt area. We will use the rail system to travel within Germany and other countries

I use vrbo.com and homeaway.com to rent apartments. For 30 days an apartment would be the way to go.

"We would be staying in the Frankfurt area. We will use the rail system to travel within Germany and other countries" There are thousands of options in the "Frankfurt area" but you aren't getting any specific town suggestions here because your travel goals from the Frankfurt area are not specific enough. What cities - (and I guess COUNTRIES?) - do you plan to visit? Their location will help determine where near Frankfurt you should start from. Will you be daytripping exclusively, or staying overnight in some of these other destinations? (I'm trying to imagine what other countries you could travel to and back from Frankfurt. Strasbourg in France, maybe? That's about 2.5 hours each way. Luxembourg is 4 hrs. each way. These would be some unusually long daytrips.) Also, what "reasonable" price do you have in mind? And do you prefer a larger place or a smaller one?

Tom, if you want to go to other countries, why do you want to stay in the same accommodation for the full 30 days? Why not stay 1 week in each country or region rather than try to do day trips to other countries?