Some wreckers can do conversion really cheap.. But they often are done poorly with low power dyno's to show for it. They may not be as reliable either. I've heard of instances where this is a mere $2000.
on the midrange level, some places do conversion for about 3.5k. These are pretty average, but a whole lot better than cheap places.
In melbourne, some places even charge 6-7k for a transplant. They do a bloody good job though. With excellent dyno results.
If you do it yourself, you'll probably end up forking 2k+ depending on wether you want to do the job properly. How many items you want to replace (e.g. Fuel lines), also, quality of the parts such as surge tanks, coil/ignitor, etc... A big part of this is the wiring. Getting an autoelectrician to do it may be best.