You are always subject to being arrested when you reenter the country. Immigration and customs officials routinely run checks on people entering the country and your warrant is likely to be discovered. If you're stopped and arrested on the warrant, you'll sit in custody until and unless bond is posted or you're shipped to the court to appear on the warrant.
If there is any way possible to get this squared away and the warrant recalled BEFORE your leave the country, do it.
Some bench warrants can be quashed (cancelled) rather easily. Running out on one could come back to haunt you. My colleague Mr. Dane is correct in saying that checks for outstanding warrants are routine, but it would also look bad during sentencing if you are convicted.
The TSA inspects the FBI database ("NCIC") and the immigration database ("NAILS") for incoming passengers. The question for you is whether a $500 bench warrant would show up in the FBI NCIC system; although I do not have access to the system I understand it does not contain state warrants for misdemeanors and failures to appear. As far as state generated records go the NCIC system only contains records related to felonies or serious misdemeanors. Check the link below for a complete list of what's on that database. Of course I can't guarantee that you won't be arrested but under the circumstances you describe the risk is minimal.