I'm going to be in Frankfurt this summer for a few days on my way back from Israel. I'd like to book a hotel (for cheap), but I'm trying to figure out where to book. I'm going to participate in the Tuesday Night Skate the night before I leave, so I'm trying to figure out whether I should stay near there (Frankfurt-Sachsenhausen), or near the kosher restaurants. Any suggestions of a cheap hotel in either area?

I have no experience along these lines (as I don't keep kosher) but you might want to check out http://www.kosherdelight.com/Germanyhotels.htm

No clue either, but you maybe someone in FRA's Jewish community (http://www.jg-ffm.de/c/cms/front_content.php) can help you out. There's a list of venues here (http://www.jg-ffm.de/c/cms/deutsch/Weitere-Adressen-in-Ffm/), but I couldn't identify any hotels or anything....

I'm going to be in Frankfurt this summer for a few days on my way back from Israel. I'd like to book a hotel (for cheap), but I'm trying to figure out where to book. I'm going to participate in the Tuesday Night Skate the night before I leave, so I'm trying to figure out whether I should stay near there (Frankfurt-Sachsenhausen), or near the kosher restaurants. Any suggestions of a cheap hotel in either area?

Try the Holiday Inn in Sachsenhausen. I have read that people got rooms for Euro 40 +. It's a pretty nice hotel on a "hill" in Sachsenhausen.
You can also try http://www.hrs.com

Well, I hear the public transportation is very good there. Does it make sense to just stay elsewhere in the city and then just take the trains to get kosher food?