Hi Wendy,
I assume someone will be fitting this for you?
Another option is to fit a replacement seal kit if the pump is just leaking, these are £24.62 + vat but there will be more labour involved but still considerably cheaper than a new pump ;)
If you are looking to source a second hand unit you may not know that Lexus now only list one pump to cover MK1 through to MK3 models.
Hope this helps,
Andy