Yeah, ed psychs are very expensive. I would ring the school and preschool and see what they actually want in terms of assessment. Across different organisations, it can range from wanting a full ed psych evaluation through to a reference from a daycare/kindy or even a parent referral. You need to clarify with them what they are wanting.

I am in NZ so not entirely sure on the Aus system but there should be a forum for gifted kids for your state and I am sure there will be people on there that know what the deal is.