Hi mate,
Funny you should ask this - I just went through the whole process myself! I had a late 2003 RX330 and had lost ALL the remote keys. I bought a blank from ebay (cost me about $65 delivered from memory). I had it cut at a local locksmith, and then used the 'Toyota Smart Keymaker' to program the immobiliser at home. I did the remote key programming dance (open door, close door, key in, key out etc etc) to program the remote itself, and it worked - to my surprise. All told, I got it working for about $110 including locksmith. The Keymaker cost me $15 or so.
One thing to note though: the car keys can operate on what appears to be two separate frequencies. I had one key blank - can't recall where it came from - that was operating at 3xx mhz, and the car wouldn't recognise the remote for programming. The one I bought that I programmed as per above was operating at 4xx mhz (I think it's 385mhz and 415mhz but don't quote me). That's a consideration for you.
I'm happy to walk you through all the processes in more detail if you decide to go down the DIY route. Or, if you're in Sydney, I'm more than happy to get together with the Keymaker and see what we can work out. Hopefully it all works out as well as it did for me.
Let me know how you get on!
D