Well, it honestly depends on how many syncros you need to replace. I had my second and third gear syncros replaced as a precaution and it ran me about $1300. Shop around, but make sure its a place that has a good reputatation and does good work...the few extra bucks may be worth it.
Your better off buying another transmission. You can take your chances on a used JDM transmission. Now would be a good time to maybe swap in another B series tranny with a lower gear ratio. Your looking at paying more to fix the one you have then buying a totally different one in most likely good condition. At the very least it'll be better than what you've got.