Like you in OZ. I sold a GIII Pilot and started to use PocketFMS, bit of dicking around, but much better system. Great forum and responses from developers usually within an hour or so (given the time differential between here and Europe).
Typical Costs:
PocketFMS Donor Registration $88
iPaq Hx4700 (new e-bay) $530
Holux GPSlim 236 BT GPS (new e-bay) $150
Ram Yoke Mount $126
Total circa: $894
Friend bought an ipaq GPS package for $350 - that would make the cost about $564. Also consider a smartphone lik the Mitac Mio A701 (from $600 to $1200 depending on how you shop). It is a triband cell phone, PDA and GPS all in one.
Just a thought,
Kevin