If you are looking for a 4 door turbo Toyota why not a Chaser(JZX100) or a Aristo? Might save you money in the long run.
I have an IS300 I find it too front heavy however there is power there when you want it and it will get you around town for under 10L/100kms. My IS300 is coming up on 300,000kms, so I am either going to swap the engine with another 2JZ-GE or 1JZGTE or 2JZGTE. The easiest swap is a 2JZ-GTE from a late model Aristo(JZS161) the loom is almost identical to a IS300 loom, however again, Auto only. There is plenty of people who have done this swap heaps of info on the net if you are willing to read it.
A Supra runs a Getrag 6 speed V160(series 1) and V161(Series 2). You could bolt these onto an IS300 however, you will need to add a clutch pedal etc and custom trans mount.
The head on a 2JZ-GE is different to the head off a 2JZ-GTE , off the shelf items for a 2JZ-GTE do not bolt onto it. These guys in the States are offering a decent turbo kit for an IS300, my friend has tuned one at 450hp and it rips http://www.swiftracing.com/SRT/item.aspx?id=10 Other than that you could look at these: http://www.boostclassifieds.com.au/advert/2230696-2000-Lexus-Is200-Sports-Luxury-Gxe10r-for-Sale.html
http://www.carsales.com.au/private/details/Lexus-IS200-2000/SSE-AD-2153169/?Cr=1
http://www.carsales.com.au/private/details/Lexus-IS200-2001/SSE-AD-2202409/?Cr=2
http://www.carsales.com.au/private/details/Lexus-IS200-2003/SSE-AD-2081665/?Cr=10
Happy Hunting....