Good luck with your legal issues, but there are alternatives.
I agree with the asskicking notion of extracting money, lol... you just need better friends to help you with this. What you really need to do is just scare the living crap outta this guy so he WANTS to give you that money, you may(could) extort more money if you really wanted to. Sure, he can call the police if he's dealing with just you but honestly you need to put him in a position where the police aren't going to be able to do anything to help him. Realistically you don't even need to have anyone rough him up, although that is always the fun way. Have someone slash his tires, break his windshield, key his car, and so on and so forth. Random vandalism like that is easy and has very low risk. Have your scariest friends, preferably ones that he knows are crazy and dangerous, just follow him around for awhile. They don't even need to say anything, just scare the living crap outta him by getting them to follow him. What can he do in a situation like that? He can call the police but all they would do is tell your friends to stop following him which they realistically don't have to do unless he goes through the trouble of getting a restraining order. You know that he knows that the police can only help him ex post facto(after the fact) so use this knowledge against him.
But then again if he knew you were good friends with some "shady" people with little regard for the law he probably would have given you the money by now, especially after just one simple threat.
Some may say that this is an immoral means to an end but isn't stealing 600+ dollars from you the initial immoral act?
EDIT: You should probably see if your legal stuff works out before taking advice given above. Actually I take that back, you need revenge for having to deal with all of this in addition to not getting the money when it was owed. But don't ever let anyone screw you over and get away with it without consequence. The guy's a little ***** and is screwing you over by working the system. When the system doesn't work properly you just gotta go around the system. This fool that's screwing you over needs to know that while the system may protect his wallet(temporarily) it won't protect HIM. Obviously crap like this pisses me off a lot. After all this crap you had to put up with you deserve more than just the money owed, he needs to know that you can't always get away with pulling crap like his. Think of it as if you are doing him a favor... teaching him a life lesson that rules are only rules and that he can't just hide behind them because guess what... they CAN be broken. You are in the right, he is in the wrong. That is the key issue here and why he deserves to face the consequences. Don't let him get away with it. Make sure you get that money back one way or another because if you don't than you are simply just another casualty of a faulty legal system. WTF how can someone default and then even have a right to appeal? That's ******** and a half.
Sorry if my advice isn't appropriate for this community, but I feel it is justifiable irreguardless of the fact that muc h of what I stated is illegal. If the law is gonna screw you outta this money you rightfully deserve, than breaking the law to get the money is perfectly reasonable... well IMO hehe.
I don't get angry very often but the crap that guy's pulling has really pissed me off, irregardless of the fact that this has nothing to do with myself whatsoever //content.invisioncic.com/y282845/emoticons/eek.gif.771b7a90cf45cabdc554ff1121c21c4a.gif