Lagrisser IV and V had greatly reduced save size from Langrisser III. Not sure why but they do.
It's a very good SLG series but there are better ones, just not on the Saturn. If you play only one game from the series I reccomend Langrisser IV. It has by far the best story and doesn't really require any background knowledge about the series to enjoy its story. The music was also some of the most amazing on the Saturn.
Langrisser IV should run about $15, maybe $20 for the LE box. Langrisser III is probably about $5-$10 (because nobody wants it once they see the gameplay). Langrisser V is about the same price as IV. The only one that will cost an arm and a leg is Dramatic Edition (Langrisser I&II) which is in the neighborhood of $35-$45.