Don't know what you'd consider "cheap", but for Ludwigsburg the most convenient one is this: NH-Hotel Ludwigsburg
It's approx. a 2-second-walk away from the venue, right across the street. Btw., the "arena" is located next to the trainstation. The station is served by lotsa local trains and our "tube", so it's quite easy to reach from the surrounding cities (like Stuttgart or Bietigheim-Bissingen), too.
A cheaper option would be (for example) the "Landgasthof Lamm" in Asperg,
approx. 5 km away from the venue. From Asperg to Ludwigsburg it's one stop via "tube" and a cab should cost 10 to 15 Euro (one way)... Public transport is between 4 and 12 Euro (return, depending on the distance).
For more info on hotels in Ludwigsburg see here: http://ludwigsburg.de/,Len/Home/Tourism/Accomodation.html
And maybe a tip for Berlin: for last years Head Cat-show i stayed at the Columbia Hotel,
pretty close to the Columbia-Halle. Nothing special, but quite reasonable priced...
Further questions regarding Ludwigsburg? Feel free to ask
Btw., the local "rock-club" is going to have an aftershow-party, no idea if it'll be any good, haven't been there for ages... http://rockfabrik-ludwigsburg.de/