I have BigDecimal objects serialized with BlazeDS to Actionscript. Once they hit Actionscript as Number objects, they have values like:
140475.32 turns
You may vote and watch the enhancement request in the Flash PLayer Jira bug tracking system at https://bugs.adobe.com/jira/browse/FP-3315
And meanwhile use the Number.toFixed() work-around see : (http://livedocs.adobe.com/flex/3/langref/Number.html#toFixed%28%29)
or use the open source implementations out there : (http://code.google.com/p/bigdecimal/) or (http://www.fxcomps.com/money.html)
As for the serialization efforts, well, it will be small if you use Blazeds or LCDS as they do support Java BigDecimal serialization (to String) cf. (http://livedocs.adobe.com/livecycle/es/sdkHelp/programmer/lcds/wwhelp/wwhimpl/common/html/wwhelp.htm?context=LiveDocs_Parts&file=serialize_data_3.html)